Use correct rebar3 command

sanmiguel · sanmiguel · commit 24973700eec4 · 2016-03-24T22:54:09.000+01:00
diff --git a/.travis.yml b/.travis.yml
@@ -9,4 +9,4 @@ otp_release:
   - 17.4
   - 17.5
   - 18.0
-script: ./rebar3 test
+script: ./rebar3 ct
