Down integrate to GitHub

Remove Required.Proto3.JsonInput.EmptyFieldMask.JsonOutput from failure list since it is now passing for Ruby

Replace SimpleItoa with StrCat in ObjectiveC compiler codes

https://groups.google.com/d/msg/protobuf/H8_D1hfg3p4/A2oPHdfUAgAJ

When compiling protobuf these produce warnings

This field isn't used yet, but it will be in the future so we don't want
to remove it. This fixes the warning in the meantime.

Down integration to GitHub

Update documentation for JavaLite

Add Mergeable config

Down integrate to Github

* external/com_google_protobuf/src/google/protobuf/stubs/strutil.cc:1122:9: runtime error: negation of -9223372036854775808 cannot be represented in type 'google::protobuf::int64' (aka 'long'); cast to an unsigned type to negate this value to itself

* Bad external/com_google_protobuf/src/google/protobuf/text_format.cc:1320:14: runtime error: null pointer passed as argument 1, which is declared to never be null
  /usr/include/string.h:62:62: note: nonnull attribute specified here
Signed-off-by: Harvey Tuch <htuch@google.com>

Merge 3.7.x into master

Also update Dockerfile for JavaScript. The old one is using an npm that is too outdated

This actually has always been using the first branch because
`__cpluscplus` is not a real definition (contrast with the real spelling
of `__cplusplus`).