Update encode64 to strict_encode64 in RequestValidator#build_signature_for (#450)

Base64#strict_encode64 takes care of removing line feeds so no character stripping is required at the end

Author: kitallis

lib/twilio-ruby/security/request_validator.rb

@@ -58,7 +58,7 @@ def build_hash_for(body)
       def build_signature_for(url, params)
         data = url + params.sort.join
         digest = OpenSSL::Digest.new('sha1')
-        Base64.encode64(OpenSSL::HMAC.digest(digest, @auth_token, data)).strip
+        Base64.strict_encode64(OpenSSL::HMAC.digest(digest, @auth_token, data))
       end
 
       private