[CONTRIBUTING.md] Remove note about semicolons

I don't much care anymore, might move to semicolon-free style in future

CONTRIBUTING.md

@@ -78,7 +78,7 @@ By contributing code to CodeMirror you
 ### Coding standards
 
 - 2 spaces per indentation level, no tabs.
-- Include semicolons after statements.
+
 - Note that the linter (`bin/lint`) which is run after each commit
   complains about unused variables and functions. Prefix their names
   with an underscore to muffle it.