Summary:
std::to_string doesn't exist on Android so don't use it.

Facebook: Did a sync to fbandroid and confirmed liger compiles with this fix.

Test Plan: existing tests

Reviewed By: ranjeeth@fb.com

Subscribers: trunkagent, folly-diffs@, shikong, kmdent, fma, pgriess

FB internal diff: D1808037

Signature: t1:1808037:1422410556:d78e0633a1554254b1a1f25bef49a4550a1817c6