Update Ubuntu images to 19.04

ci/docker/aarch64-linux-android/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN dpkg --add-architecture i386 && \
     apt-get update && \

ci/docker/aarch64-unknown-linux-gnu/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 RUN apt-get update && apt-get install -y --no-install-recommends \
   gcc libc6-dev ca-certificates \
   gcc-aarch64-linux-gnu libc6-dev-arm64-cross qemu-user

ci/docker/aarch64-unknown-linux-musl/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
   gcc make libc6-dev git curl ca-certificates \

ci/docker/arm-linux-androideabi/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN dpkg --add-architecture i386 && \
     apt-get update && \

ci/docker/arm-unknown-linux-gnueabihf/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 RUN apt-get update && apt-get install -y --no-install-recommends \
   gcc libc6-dev ca-certificates \
   gcc-arm-linux-gnueabihf libc6-dev-armhf-cross qemu-user

ci/docker/arm-unknown-linux-musleabihf/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
   gcc make libc6-dev git curl ca-certificates \

ci/docker/asmjs-unknown-emscripten/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \

ci/docker/i686-linux-android/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN dpkg --add-architecture i386 && \
     apt-get update && \

ci/docker/i686-unknown-linux-gnu/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 RUN apt-get update
 RUN apt-get install -y --no-install-recommends \
   gcc-multilib libc6-dev ca-certificates

ci/docker/i686-unknown-linux-musl/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN dpkg --add-architecture i386
 RUN apt-get update

ci/docker/mips-unknown-linux-gnu/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         gcc libc6-dev qemu-user ca-certificates \

ci/docker/mips-unknown-linux-musl/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         gcc libc6-dev qemu-user ca-certificates qemu-system-mips curl \

ci/docker/mips64-unknown-linux-gnuabi64/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         gcc libc6-dev qemu-user ca-certificates \

ci/docker/mips64el-unknown-linux-gnuabi64/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         gcc libc6-dev qemu-user ca-certificates \

ci/docker/mipsel-unknown-linux-musl/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         gcc libc6-dev qemu-user ca-certificates qemu-system-mips curl \

ci/docker/powerpc-unknown-linux-gnu/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         gcc libc6-dev qemu-user ca-certificates \

ci/docker/powerpc64-unknown-linux-gnu/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         gcc libc6-dev qemu-user ca-certificates \

ci/docker/powerpc64le-unknown-linux-gnu/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         gcc libc6-dev qemu-user ca-certificates \

ci/docker/s390x-unknown-linux-gnu/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         curl ca-certificates \

ci/docker/sparc64-unknown-linux-gnu/Dockerfile

-FROM ubuntu:18.04
+FROM ubuntu:19.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         curl ca-certificates \