(legacy burden) upgrade thrift/lib/java/maven/pom.xml to jdk8
(legacy burden) upgrade thrift/lib/java/maven/pom.xml to jdk8

Summary:Having a secondary build here is possibly a bad idea and a legacy burden, but
for the purpose of pushing the jdk8 migrations forward upgrade it to jdk8 since
it builds successfully in origin/master.

Reviewed By: skreyen

Differential Revision: D3150604

fb-gh-sync-id: c992c2b6fe52f0196bd56c88b1ccad006ede482d
fbshipit-source-id: c992c2b6fe52f0196bd56c88b1ccad006ede482d

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