Requiring PCRE >= 7.0

There is a bug in libpcre < 7.0 that causes preg compilation errors that break
mockery. Libpcre >= 7.0 should fix this issue according to their changelog, but
the author has only tested on libpcre 8.31.
Merge pull request #146 from QuickenLoans/master

Requiring libpcre >= 7.0