install gpg in travis.

.travis.yml

@@ -29,7 +29,7 @@ matrix:
     #  sudo: true
 
 install:
-  - travis_retry pip install -U pip coverage codecov flake8 $TEST_REQUIRE
+  - travis_retry pip install -U pip coverage codecov flake8 gpg $TEST_REQUIRE
 
 script:
   # Test without c extensions