diff --git a/.rubocop.yml b/.rubocop.yml
index 8dbbbf0..9b181f8 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -38,5 +38,8 @@ Style/SpaceInsideHashLiteralBraces:
 Style/StringLiterals:
   EnforcedStyle: double_quotes
 
-Style/TrailingComma:
+Style/TrailingCommaInLiteral:
+  EnforcedStyleForMultiline: 'comma'
+
+Style/TrailingCommaInArguments:
   EnforcedStyleForMultiline: 'comma'
diff --git a/.travis.yml b/.travis.yml
index d2e47a0..0948e67 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,6 +9,7 @@ rvm:
   - 2.0.0
   - 2.1
   - 2.2
+  - 2.3.0
   - jruby-18mode
   - jruby-19mode
   - jruby-head
@@ -16,7 +17,8 @@ rvm:
   - ruby-head
 matrix:
   allow_failures:
-    - rvm: jruby-head
-    - rvm: ruby-head
+    - rvm: 1.8.7
+    - rvm: jruby-18mode
   fast_finish: true
+cache: bundler
 sudo: false
diff --git a/Gemfile b/Gemfile
index 8b100f4..e079ae7 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,16 +1,16 @@
-source "http://rubygems.org"
+source "https://rubygems.org"
 
 gem "rake"
 
 group :test do
   gem "coveralls"
   gem "json", :platforms => [:jruby, :ruby_18, :ruby_19]
-  gem "mime-types", "~> 1.25", :platforms => [:jruby, :ruby_18]
+  gem "mime-types", :platforms => [:jruby, :ruby_18]
   gem "rack-test"
-  gem "rest-client", "~> 1.6.0", :platforms => [:jruby, :ruby_18]
-  gem "rspec", "~> 3.2"
-  gem "rubocop", ">= 0.30", :platforms => [:ruby_19, :ruby_20, :ruby_21, :ruby_22]
-  gem "simplecov", ">= 0.9"
+  gem "rest-client", :platforms => [:jruby, :ruby_18]
+  gem "rspec"
+  gem "rubocop", :platforms => [:ruby_19, :ruby_20, :ruby_21, :ruby_22]
+  gem "simplecov"
   gem "webmock"
 end
 
diff --git a/lib/omniauth-oauth2/version.rb b/lib/omniauth-oauth2/version.rb
index 5a79a34..058af9b 100644
--- a/lib/omniauth-oauth2/version.rb
+++ b/lib/omniauth-oauth2/version.rb
@@ -1,5 +1,6 @@
+# frozen_string_literal: true
 module OmniAuth
   module OAuth2
-    VERSION = "1.4.0"
+    VERSION = "1.4.0".freeze
   end
 end
diff --git a/lib/omniauth/strategies/oauth2.rb b/lib/omniauth/strategies/oauth2.rb
index 3ffff1b..34a238e 100644
--- a/lib/omniauth/strategies/oauth2.rb
+++ b/lib/omniauth/strategies/oauth2.rb
@@ -38,9 +38,9 @@ def client
 
       credentials do
         hash = {"token" => access_token.token}
-        hash.merge!("refresh_token" => access_token.refresh_token) if access_token.expires? && access_token.refresh_token
-        hash.merge!("expires_at" => access_token.expires_at) if access_token.expires?
-        hash.merge!("expires" => access_token.expires?)
+        hash["refresh_token"] = access_token.refresh_token if access_token.expires? && access_token.refresh_token
+        hash["expires_at"] = access_token.expires_at if access_token.expires?
+        hash["expires"] = access_token.expires?
         hash
       end
 
diff --git a/omniauth-oauth2.gemspec b/omniauth-oauth2.gemspec
index 53983a4..8224d91 100644
--- a/omniauth-oauth2.gemspec
+++ b/omniauth-oauth2.gemspec
@@ -6,7 +6,7 @@ Gem::Specification.new do |gem|
   gem.add_dependency "oauth2",     "~> 1.0"
   gem.add_dependency "omniauth",   "~> 1.2"
 
-  gem.add_development_dependency "bundler", "~> 1.0"
+  gem.add_development_dependency "bundler"
 
   gem.authors       = ["Michael Bleigh", "Erik Michaels-Ober"]
   gem.email         = ["michael@intridea.com", "sferik@gmail.com"]