Log Message:
Update to 4.0.7

CHANGELOG:
4.0.7
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* Removed dependency on `constraints`. It was used in a pre-release version of
  4.0 but never made it into 4.0, but the dependency had remained around
  complicating builds for GHC 7.4.

4.0.6
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* `makeLenses` attempt to make the accessors it can under existential
  quantification.
* Added `(&~)`.
* _Experimental_ support for parallel builds on GHC 7.8 with
  `cabal install lens -fj`. Due to at last one known issue with GHC, it isn't
  recommended to use this option when rebuilding lens, as a race condition on
  at least one platform has been seen in the wild.
* Added `RoleAnnotations` for GHC 7.8.1. These rule out a few user-accessible
  bottoms that could be caused by creative abuse of the new `Coercible`
  machinery. However, there was no `unsafeCoerce` exposed.
* Removed some impossible cases that required unwritable instances from 
  the example doctypes.