Comment out boot cucumber tests

This is in response to the slowness noticed over the last few days and
unrelated changes causing travis failures. For example:

rapid7#4252 (comment)

Author: Tod Beardsley

.travis.yml

@@ -1,6 +1,7 @@
 env:
   - RAKE_TASK=cucumber
-  - RAKE_TASK=cucumber:boot
+# Commenting out the boot tests due to chronic timeouts.
+#  - RAKE_TASK=cucumber:boot
   - RAKE_TASK=spec SPEC_OPTS="--tag content"
   - RAKE_TASK=spec SPEC_OPTS="--tag ~content"