Update circleci config to test multiple go versions

Author: belak

circle.yml

@@ -1,10 +1,26 @@
-version: 2.0
+version: 2
 jobs:
-  build:
+  build-go-latest:
+    docker:
+    - image: golang:latest
+    working_directory: /go/src/github.com/gliderlabs/ssh
+    steps:
+    - checkout
+    - run: go get
+    - run: go test -v -race
+
+  build-go-1.7:
     docker:
-    - image: golang:1.10
+    - image: golang:1.7
     working_directory: /go/src/github.com/gliderlabs/ssh
     steps:
     - checkout
     - run: go get
     - run: go test -v -race
+
+workflows:
+  version: 2
+  build:
+    jobs:
+      - build-go-latest
+      - build-go-1.7