Update Parser gem

We're a point release behind, and this provides improvements around
parsing `&.` See [full changes][1].

[1]: whitequark/parser@v2.3.3.1...v2.4.0.0

Author: wfleming

Gemfile

@@ -3,7 +3,7 @@
 source 'https://rubygems.org'
 
 gem "activesupport", require: false
-gem "parser", "~> 2.3.3.1"
+gem "parser", "~> 2.4.0"
 gem "pry", require: false
 gem "rubocop", "~> 0.45", require: false
 gem "rubocop-migrations", require: false

Gemfile.lock

@@ -13,7 +13,7 @@ GEM
     i18n (0.7.0)
     method_source (0.8.2)
     minitest (5.10.1)
-    parser (2.3.3.1)
+    parser (2.4.0.0)
       ast (~> 2.2)
     powerpack (0.1.1)
     pry (0.10.4)
@@ -58,7 +58,7 @@ PLATFORMS
 
 DEPENDENCIES
   activesupport
-  parser (~> 2.3.3.1)
+  parser (~> 2.4.0)
   pry
   rake
   rspec
@@ -68,4 +68,4 @@ DEPENDENCIES
   safe_yaml
 
 BUNDLED WITH
-   1.13.6
+   1.15.4