[Fix #1485] Ignore procs in SymbolProc

A Rails-specific fix. See https://github.com/bbatsov/rubocop/issues/1485
for details.
[Fix #1473] Recognize operator []= in MultilineOperationIndentation

The []= operator is a form of assignment and should be
recognized as such in MultilineOperationIndentation where
assignment is handled in a special way.
Merge pull request #1486 from jonas054/1473_MultilineOperationIndentation_bug

[Fix #1473] Recognize operator []= in MultilineOperationIndentation
[Fix #1445] Allow sprockets directive comments in Style/LeadingCommentSpace
Cut 0.28.0