Update cld3 to 3.1.1 (#2958)

According to the release message:
> Fix for macOS and minor improvements

Gemfile.lock

@@ -99,7 +99,7 @@ GEM
       rack-test (>= 0.5.4)
       xpath (~> 2.0)
     chunky_png (1.3.8)
-    cld3 (3.1.0)
+    cld3 (3.1.1)
       ffi (>= 1.1.0, < 1.10.0)
     climate_control (0.1.0)
     cocaine (0.5.8)