chore: release 1.15.0

[release-please]

🤖 I have created a release *beep* *boop*

1.15.0 (2021-03-10)

Features

• allow_alias for enums (#207) (6d4d713)

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This PR was generated with Release Please. See documentation.

[codecov]

Codecov Report

Merging #208 (3a39015) into master (6a43682) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #208   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           20        20           
  Lines          862       886   +24     
  Branches       149       160   +11     
=========================================
+ Hits           862       886   +24     

Impacted Files	Coverage Δ
proto/modules.py	100.00% <ø> (ø)
proto/enums.py	100.00% <100.00%> (ø)
proto/marshal/collections/repeated.py	100.00% <100.00%> (ø)
proto/marshal/marshal.py	100.00% <100.00%> (ø)

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[yoshi-automation]

Release is at https://github.com/googleapis/proto-plus-python/releases/tag/v1.15.0