Upgrade whitequark/parser to 2.5.3.0

This squelches the following warning:

warning: parser/current is loading parser/ruby24, which recognizes
warning: 2.4.4-compliant syntax, but you are running 2.4.5.
warning: please see https://github.com/whitequark/parser#compatibility-with-ruby-mri.

Gemfile.lock

@@ -547,7 +547,7 @@ GEM
     orm_adapter (0.5.0)
     os (1.0.0)
     parallel (1.12.1)
-    parser (2.5.1.2)
+    parser (2.5.3.0)
       ast (~> 2.4.0)
     parslet (1.8.2)
     peek (1.0.1)