Update license headers

[michaelbausor]

Update license headers to match those generated by toolkit

[codecov-io]

Codecov Report

Merging #487 into master will not change coverage.
The diff coverage is n/a.

@@ Coverage Diff @@## master #487 +/- ##
=========================================
Coverage 70.33% 70.33% Complexity 775 775 =========================================
Files 163 163 Lines 3668 3668 Branches 273 273 =========================================
Hits 2580 2580 Misses 973 973 Partials 115 115

Impacted Files	Coverage Δ	Complexity Δ
...java/com/google/api/gax/grpc/GrpcCallSettings.java	70% <ø> (ø)	5 <0> (ø)	⬇️
...main/java/com/google/api/gax/rpc/ServerStream.java	81.81% <ø> (ø)	5 <0> (ø)	⬇️
.../com/google/api/gax/grpc/GrpcTransportChannel.java	72.22% <ø> (ø)	9 <0> (ø)	⬇️
...ain/java/com/google/api/gax/rpc/BatchedFuture.java	100% <ø> (ø)	4 <0> (ø)	⬇️
.../gax/retrying/ServerStreamingAttemptException.java	100% <ø> (ø)	3 <0> (ø)	⬇️
...le/api/gax/core/BackgroundResourceAggregation.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...oogle/api/gax/httpjson/HttpJsonDirectCallable.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...om/google/api/gax/rpc/ApiResultRetryAlgorithm.java	92.3% <ø> (ø)	7 <0> (ø)	⬇️
...om/google/api/gax/batching/BatchingThresholds.java	80% <ø> (ø)	1 <0> (ø)	⬇️
...ax/src/main/java/com/google/api/gax/rpc/Batch.java	100% <ø> (ø)	7 <0> (ø)	⬇️
... and 153 more

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[garrettjonesgoogle]

LGTM