travis: add logo to README, switch to go 1.4/1.5

.travis.yml

@@ -1,9 +1,10 @@
 language: go
 go:
-  - 1.3
+  - 1.4
+  - 1.5
 
 install:
- - go get code.google.com/p/go.tools/cmd/cover
+ - go get golang.org/x/tools/cmd/cover 
 
 script:
  - ./test

README.md

@@ -2,6 +2,8 @@
 
 ![flannel Logo](logos/flannel-horizontal-color.png)
 
+[![Build Status](https://travis-ci.org/coreos/flannel.png?branch=master)](https://travis-ci.org/coreos/flannel)
+
 flannel is a virtual network that gives a subnet to each host for use with container runtimes.
 
 Platforms like Google's Kubernetes assume that each container (pod) has a unique, routable IP inside the cluster.