Add Travis CI integration with ESnet's Slack.

.travis.yml

@@ -6,4 +6,8 @@ os:
    - linux
    - osx
  
+notifications:
+  slack:
+    secure: ImUmX7hcYotHWCDBfOcIvF6H7kkeGqiaUCy7SVPFtgPbz33ttpbRd94E7oxWVmZMLKb+i6+JCujTEWGwGBimzH+DjL0LLWs0ShzXZIUa1UzEPTc4hgV6VAxucYKFg2WrbXgOPWbulkMG1VZ6pX7GlAEGf0qyNqn44F7S2ay9m18=
+
 script: ./configure && make && make check