Attempting to use other keyserver, as we see failure from Travis fetching

.travis.yml

@@ -17,7 +17,7 @@ before_install:
   # See: https://github.com/travis-ci/travis-ci/issues/1986
   #
   - sudo sed -i -e s/table_cache/table_open_cache/ -e /log_slow_queries/d /etc/mysql/my.cnf
-  - sudo apt-key adv --keyserver pgp.mit.edu --recv-keys 5072E1F5
+  - sudo apt-key adv --keyserver subkeys.pgp.net --recv-keys 5072E1F5
   - sudo add-apt-repository 'deb http://repo.mysql.com/apt/ubuntu/ precise mysql-5.6'
   - sudo apt-get -qq update
   - sudo apt-get -qq -o Dpkg::Options::=--force-confold install mysql-server-5.6