build: update travis CI config

This commit updates the previous travis CI config to pin against the
two latest golang versions, and perform installation via Glide.

Additionally, this should allow lnwallet’s integration tests to build
properly as the btcd binary will be available in the build process’
PATH.

.travis.yml

@@ -1,4 +1,12 @@
 language: go
-
 go:
-        - tip
+  - 1.5.4
+  - 1.6.3
+sudo: false
+install:
+  - go get -v github.com/roasbeef/btcd # Required for the rpc test package.
+  - go get -v github.com/Masterminds/glide
+  - glide install
+script:
+  - export PATH=$PATH:$HOME/gopath/bin
+  - export GO15VENDOREXPERIMENT=1