chore: release 6.0.0

[release-please]

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

6.0.0 (2021-03-21)

⚠ BREAKING CHANGES

• add closeAsync() method to Connection (feat!: add closeAsync() method to Connection #984)
• drops support of Java 7 (feat!: drops support of Java 7 #946)
• customer-managed encryption keys for Spanner (feat!: customer-managed encryption keys for Spanner #666)

Features

• add closeAsync() method to Connection (#984) (e7ec96e)
• customer-managed encryption keys for Spanner (#666) (8338116)
• drops support of Java 7 (#946) (7af1951)

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[codecov]

Codecov Report

Merging #994 (d20b988) into master (1110700) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #994      +/-   ##
============================================
- Coverage     85.11%   85.08%   -0.03%     
+ Complexity     2619     2616       -3     
============================================
  Files           154      154              
  Lines         14319    14319              
  Branches       1331     1331              
============================================
- Hits          12187    12183       -4     
- Misses         1567     1570       +3     
- Partials        565      566       +1     

Impacted Files	Coverage Δ	Complexity Δ
.../google/cloud/spanner/AbstractLazyInitializer.java	92.85% <0.00%> (-7.15%)	4.00% <0.00%> (-1.00%)
...ain/java/com/google/cloud/spanner/SessionPool.java	88.73% <0.00%> (-0.59%)	71.00% <0.00%> (-2.00%)
...a/com/google/cloud/spanner/SessionPoolOptions.java	69.53% <0.00%> (ø)	17.00% <0.00%> (-1.00%)
...m/google/cloud/spanner/connection/SpannerPool.java	87.89% <0.00%> (+0.52%)	33.00% <0.00%> (ø%)
...ud/spanner/SessionPoolAsyncTransactionManager.java	87.21% <0.00%> (+1.50%)	14.00% <0.00%> (+2.00%)

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[yoshi-automation]

🤖 Release is at https://github.com/googleapis/java-spanner/releases/tag/v6.0.0 🌻

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