[Fix #1339] Handle eql? and equal? in OpMethod
Fix a typo
Code style
[Fix #1340] Handle call with no receiver correctly

For blocks with an unused argument which call a method with no explicit
receiver, the Style/SymbolProc would attempt to check 'receiver.type'
and crash because receiver is nil.
Fix new Rubocop violation on cyclomatic complexity

Checking for nil receiver was the straw that broke the camel's back.
Refactored the Style/SymbolProc cop to use #can_shorten? to analyse a
block and its arguments to determine if it fits the pattern.
Update CHANGELOG.md for Style/SymbolProc bugfix