Run integration tests via Travis

Mail from the Travis team:

Thanks for the email. I have set up s3fs-fuse/s3fs-fuse with our alpha
testing stack which may allow you to use FUSE.

To use it, add the following to your .travis.yml:
dist: trusty

Please keep in mind that the service may become unavailable without
notice, and change details. We welcome your feedback as to what works
and what does not with this setup.

.travis.yml

@@ -1,4 +1,5 @@
 language: cpp
+dist: trusty
 cache: apt
 before_install:
  - sudo apt-get update -qq
@@ -8,8 +9,7 @@ script:
  - ./configure
  - make
  - make check -C src
-# TODO: Travis does not support FUSE so integration tests cannot run:
-# https://github.com/travis-ci/travis-ci/issues/1100
-#after_script:
-#  - modprobe fuse
-#  - make check -C test
+ # Travis granted s3fs access to their upcoming alpha testing stack which may
+ # allow us to use FUSE.
+ - modprobe fuse
+ - make check -C test