Added libgtest-dev install to Travis
Added libgtest-dev install to Travis

npapa/TileDB,TileDB-Inc/TileDB,npapa/TileDB,Intel-HLS/TileDB,kavskalyan/TileDB,Intel-HLS/TileDB,TileDB-Inc/TileDB,TileDB-Inc/TileDB,kavskalyan/TileDB,TileDB-Inc/TileDB