Update cucumber version

Version 1.3.10 has problems running with Ruby 2.2.3 - `undefined method `unpack' for nil:NilClass (NoMethodError)`
Updating the cucumber version fixes this error.

See: cucumber/cucumber-ruby#781

Gemfile

@@ -1,7 +1,7 @@
 source "https://rubygems.org"
 
 gem "capybara", "2.1.0"
-gem "cucumber", "1.3.10"
+gem "cucumber", "1.3.20"
 gem "launchy", "2.4.2"
 gem "nokogiri", "1.6.1"
 gem "rake", "10.1.1"

Gemfile.lock

@@ -17,12 +17,12 @@ GEM
       ffi (~> 1.0, >= 1.0.11)
     cliver (0.3.2)
     colored (1.2)
-    cucumber (1.3.10)
+    cucumber (1.3.20)
       builder (>= 2.1.2)
       diff-lcs (>= 1.1.3)
       gherkin (~> 2.12)
       multi_json (>= 1.7.5, < 2.0)
-      multi_test (>= 0.0.2)
+      multi_test (>= 0.1.2)
     diff-lcs (1.2.5)
     ffi (1.9.10)
     gherkin (2.12.2)
@@ -78,7 +78,7 @@ PLATFORMS
 DEPENDENCIES
   capybara (= 2.1.0)
   capybara-screenshot (= 1.0.3)
-  cucumber (= 1.3.10)
+  cucumber (= 1.3.20)
   json (= 1.8.2)
   launchy (= 2.4.2)
   nokogiri (= 1.6.1)
@@ -89,3 +89,6 @@ DEPENDENCIES
   rspec (= 2.14.1)
   selenium-webdriver (= 2.47.1)
   test-unit (= 3.0.9)
+
+BUNDLED WITH
+   1.10.6