Fix things I didn't break to shut up Rubocop

Author: knu

lib/omniauth-oauth2/version.rb

@@ -1,5 +1,5 @@
 module OmniAuth
   module OAuth2
-    VERSION = "1.4.0"
+    VERSION = "1.4.0".freeze
   end
 end

lib/omniauth/strategies/oauth2.rb

@@ -56,9 +56,9 @@ def query_string
 
       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