Update webmock to get rid of error
Update webmock to get rid of error

I was seeing

 unknown keyword: write_timeout

As a failure for http specs in 2.6.0. The issue was webmock. Upgrading webmock fixes ruby 2.6.0+ support and makes the specs pass.

I also upgraded rake for other reasons. Not particularly necessary but shouldn't hurt anything either.

jnunemaker/flipper,jnunemaker/flipper,jnunemaker/flipper,jnunemaker/flipper