[build] set up Travis CI to run the unit tests

This commit sets up Travis CI to run the unit tests.
It installs glide, initializes the vendor directory,
and then runs `make test`.

.travis.yml

@@ -0,0 +1,23 @@
+language: go
+
+go:
+- 1.8
+
+# blech, Travis downloads with capitals in DirectXMan12, which confuses go
+go_import_path: github.com/directxman12/k8s-prometheus-adapter
+
+addons:
+  apt:
+    sources:
+    - sourceline: 'ppa:masterminds/glide'
+    packages:
+    - glide
+
+install:
+- make -B vendor
+
+script: make test
+
+cache:
+  directories:
+  - ~/.glide