Update to active_support 4.2.4

[MichaelSp]

Minitest::UnexpectedError: ArgumentError: wrong number of arguments (2 for 1)
    /home/michael/.rbenv/versions/2.2.2/lib/ruby/gems/2.2.0/gems/filewatch-0.6.4/lib/filewatch/helper.rb:19:in `atomic_write'
    /home/michael/.rbenv/versions/2.2.2/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/cache/file_store.rb:83:in `write_entry'

Current version of active_support (4.2.4) uses 2 arguments.
Result is that filewatch is incompatible with active_support 4.2.4

fixes #67

[jsvd]

To avoid further conflicts, I'd suggest changing the namespace of this method to FileWatch or FileWatch::File, what do you think @MichaelSp ?

[MichaelSp]

Yes, sounds like a plan.

[MichaelSp]

anything I can do to get this released?

[guyboertje]

@MichaelSp - this has been implemented in this PR along with a bunch of other overdue changes...
See https://github.com/jordansissel/ruby-filewatch/pull/79/files#diff-d5c5655c1c01ef1837bf4fa11533221cR7

We just need some developer time to complete the PR review cycle.