Use strict_encode64 if possible

Author: pitbulk

lib/onelogin/ruby-saml/saml_message.rb

@@ -121,7 +121,11 @@ def decode(string)
       # @return [String] The encoded string
       #
       def encode(string)
-        Base64.encode64(string).gsub(/\n/, "")
+        if Base64.respond_to?('strict_encode64')
+          Base64.strict_encode64(string)
+        else
+          Base64.encode64(string).gsub(/\n/, "")
+        end
       end
 
       # Check if a string is base64 encoded