Update Travis CI configuration

* Use Ubuntu 14.04 with Docker.
* Use latest patch versions of Go.
* Replace hacks for forks with an official solution.

.travis.yml

@@ -1,12 +1,15 @@
+dist: trusty
 sudo: false
 
 language: go
 
 go:
-  - 1.6
-  - 1.7
-  - 1.8
-  - tip
+  - 1.6.x
+  - 1.7.x
+  - 1.8.x
+  - master
+
+go_import_path: github.com/smira/aptly
 
 addons:
   apt:
@@ -20,9 +23,6 @@ env:
     - secure: "V7OjWrfQ8UbktgT036jYQPb/7GJT3Ol9LObDr8FYlzsQ+F1uj2wLac6ePuxcOS4FwWOJinWGM1h+JiFkbxbyFqfRNJ0jj0O2p93QyDojxFVOn1mXqqvV66KFqAWR2Vzkny/gDvj8LTvdB1cgAIm2FNOkQc6E1BFnyWS2sN9ea5E="
     - secure: "OxiVNmre2JzUszwPNNilKDgIqtfX2gnRSsVz6nuySB1uO2yQsOQmKWJ9cVYgH2IB5H8eWXKOhexcSE28kz6TPLRuEcU9fnqKY3uEkdwm7rJfz9lf+7C4bJEUdA1OIzJppjnWUiXxD7CEPL1DlnMZM24eDQYqa/4WKACAgkK53gE="
 before_install:
-  - mkdir -p $GOPATH/src/github.com/smira
-  - mv $TRAVIS_BUILD_DIR $GOPATH/src/github.com/smira || true
-  - cd $GOPATH/src/github.com/smira/aptly
   - virtualenv system/env
   - . system/env/bin/activate
   - pip install six packaging appdirs
@@ -36,7 +36,7 @@ script: make travis
 
 matrix:
     allow_failures:
-        - go: tip
+        - go: master
 
 notifications:
   webhooks: