Revert "upgrade com.google.code.gson to 2.6 version"
Revert "upgrade com.google.code.gson to 2.6 version"

This reverts commit 93b97e9cc12bdaea1fe90e146ffabe719a162fac.

(sapling split of 45c3b31e16cb278171f3b05d810ee4669a4171e9)
foursquare/fsqio,foursquare/fsqio,foursquare/fsqio,foursquare/fsqio,foursquare/fsqio