chore: release 4.0.0

[bcoe]

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

4.0.0 (2019-05-15)

Bug Fixes

• deps: update dependency google-gax to v1 (#402) (547f1a1)
• correct Long types import (#358) (dfe1def)
• DEADLINE_EXCEEDED is no longer retried (47eedf0)
• DEADLINE_EXCEEDED retry code is idempotent (#403) (2a7c3ab)
• deps: update dependency @google-cloud/projectify to v1 (#391) (761896b)
• deps: update dependency @google-cloud/promisify to v1 (#392) (94a45bd)
• deps: update dependency arrify to v2 (2b47d10)
• deps: update dependency google-auth-library to v4 (#400) (19bc787)
• deps: update dependency google-gax to ^0.26.0 (#386) (29b81e3)
• include 'x-goog-request-params' header in requests (#372) (d91be05)
• lint (#384) (9a4d746)
• docs: move ts overloads above doc string (#356) (a7f1123)

Build System

• upgrade engines field to >=8.10.0 (#388) (a8cf59f)

BREAKING CHANGES

• upgrade engines field to >=8.10.0 (build!: upgrade engines field to >=8.10.0 #388)

[codecov]

Codecov Report

Merging #407 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #407   +/-   ##
=======================================
  Coverage   98.05%   98.05%           
=======================================
  Files           5        5           
  Lines         617      617           
  Branches      145      145           
=======================================
  Hits          605      605           
  Partials       12       12

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[yoshi-automation]

Release is at https://github.com/googleapis/nodejs-datastore/releases/tag/v4.0.0

[yoshi-automation]

The release build has started, the log can be viewed here. 🌻

[yoshi-automation]

🥚 You hatched a release! The release build finished successfully! 💜