set PHP_VERSION to 5.6

Summary: Now that @elgenie landed splats and variadics, we are feature complete with 5.6.
Closes #3003

Reviewed By: joelm, smith, eletuchy, liranuna

Differential Revision: D1426390
get us compiling on travis

Summary: They are using an older version of libsqlite3, which our make files don't reject, but we end up not compiling. This is the easiest fix.

Reviewed By: @JoelMarcey

Differential Revision: D1428652