Make dependency on preggy explicit
Make dependency on preggy explicit

Preggy is used a bunch in the Thumbor tests. It probably works right now because some sub-dependencies of Thumbor depend on it too.
However, minimum version is important, since the test_load_with_utf8_url test in tests.loaders.test_http_loader.HttpLoaderTestCase relies on error_not_to_happen, which was introduced in Preggy 1.3.0.
fanhero/thumbor,fanhero/thumbor,fanhero/thumbor,fanhero/thumbor