Update charlock_holmes to 0.76

Didn't compile against newer icu4c versions and was fixed upstream in
https://github.com/brianmario/charlock_holmes/pull/129, which was
releaed in the versions its now locked to.

Gemfile.lock

@@ -120,7 +120,7 @@ GEM
       activesupport (>= 4.0.0)
       mime-types (>= 1.16)
     cause (0.1)
-    charlock_holmes (0.7.5)
+    charlock_holmes (0.7.6)
     childprocess (0.7.0)
       ffi (~> 1.0, >= 1.0.11)
     chronic (0.10.2)