Fix check for forwarding env var

Apparently `present?` wasn't available probably because it's an
ActiveSupport thing. Now parsing the phone number as an integer to
validate the format.

Author: gaffneyc

views/welcome.builder

@@ -1,6 +1,6 @@
-if ENV["FORWARD_PHONE_TO"].present?
+if ENV.fetch("FORWARD_PHONE_TO", false)
   # Number must include area code and not have any other special characters.
-  xml.Dial ENV["FORWARD_PHONE_TO"]
+  xml.Dial Integer(ENV["FORWARD_PHONE_TO"]).to_s
 else
   xml.Gather timeout: 5, action: "/menu", numDigits: "1" do |g|
     g.Play sound_url("welcome")