Re-enable linux on travis
Re-enable linux on travis

Summary: Travis clang issue on linux is fixed now, re-enable linux on travis

Test Plan: https://travis-ci.org/facebook/rocksdb/builds/141098948

Reviewers: yiwu, sdong, yhchiang, andrewkr

Reviewed By: andrewkr

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D60189

vmx/rocksdb,hobinyoon/rocksdb,Andymic/rocksdb,ryneli/rocksdb,vmx/rocksdb,wat-ze-hex/rocksdb,ryneli/rocksdb,facebook/rocksdb,wat-ze-hex/rocksdb,norton/rocksdb,tsheasha/rocksdb,norton/rocksdb,hobinyoon/rocksdb,vmx/rocksdb,SunguckLee/RocksDB,tsheasha/rocksdb,wat-ze-hex/rocksdb,bbiao/rocksdb,facebook/rocksdb,wenduo/rocksdb,SunguckLee/RocksDB,tsheasha/rocksdb,OverlordQ/rocksdb,OverlordQ/rocksdb,bbiao/rocksdb,facebook/rocksdb,OverlordQ/rocksdb,bbiao/rocksdb,SunguckLee/RocksDB,vmx/rocksdb,wenduo/rocksdb,facebook/rocksdb,wenduo/rocksdb,SunguckLee/RocksDB,tsheasha/rocksdb,wat-ze-hex/rocksdb,ryneli/rocksdb,jalexanderqed/rocksdb,wenduo/rocksdb,wenduo/rocksdb,SunguckLee/RocksDB,OverlordQ/rocksdb,ryneli/rocksdb,hobinyoon/rocksdb,OverlordQ/rocksdb,norton/rocksdb,norton/rocksdb,Andymic/rocksdb,Andymic/rocksdb,jalexanderqed/rocksdb,tsheasha/rocksdb,bbiao/rocksdb,tsheasha/rocksdb,facebook/rocksdb,vmx/rocksdb,hobinyoon/rocksdb,jalexanderqed/rocksdb,norton/rocksdb,tsheasha/rocksdb,ryneli/rocksdb,facebook/rocksdb,Andymic/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,wat-ze-hex/rocksdb,bbiao/rocksdb,bbiao/rocksdb,norton/rocksdb,ryneli/rocksdb,OverlordQ/rocksdb,wat-ze-hex/rocksdb,Andymic/rocksdb,norton/rocksdb,hobinyoon/rocksdb,jalexanderqed/rocksdb,facebook/rocksdb,hobinyoon/rocksdb,vmx/rocksdb,jalexanderqed/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,wenduo/rocksdb,facebook/rocksdb,vmx/rocksdb,Andymic/rocksdb,OverlordQ/rocksdb,SunguckLee/RocksDB,tsheasha/rocksdb,bbiao/rocksdb,wat-ze-hex/rocksdb,wenduo/rocksdb,wenduo/rocksdb,norton/rocksdb,vmx/rocksdb,wat-ze-hex/rocksdb,jalexanderqed/rocksdb,hobinyoon/rocksdb,bbiao/rocksdb,ryneli/rocksdb,hobinyoon/rocksdb,jalexanderqed/rocksdb