use go1.5 for circleCI (snippet from circle support)

License: MIT
Signed-off-by: Jeromy <jeromyj@gmail.com>

circle.yml

@@ -3,11 +3,17 @@ machine:
     TEST_NO_FUSE: 1
     TEST_VERBOSE: 1
     TRAVIS: 1
+  post:
+    - sudo rm -rf /usr/local/go
+    - if [ ! -e go1.5.linux-amd64.tar.gz ]; then curl -o go1.5.linux-amd64.tar.gz https://storage.googleapis.com/golang/go1.5.linux-amd64.tar.gz; fi
+    - sudo tar -C /usr/local -xzf go1.5.linux-amd64.tar.gz
 
 dependencies:
   pre:
     # setup ipv6
     - sudo sysctl -w net.ipv6.conf.lo.disable_ipv6=0 net.ipv6.conf.default.disable_ipv6=0 net.ipv6.conf.all.disable_ipv6=0
+  cache_directories:
+    - ~/go1.5.linux-amd64.tar.gz
 
 test:
   override: