Bump Go release version in travis conf

Missed this when bumping the Go version Travis uses

Author: wjdp

.travis.yml

@@ -1,5 +1,6 @@
 language: go
 
+# When upgrading Go version also change deploy > provider > on > go at the bottom of this file.
 go:
 - 1.8.3
 
@@ -34,7 +35,7 @@ deploy:
     on:
       tags: true
       repo: wjdp/htmltest
-      go: 1.7.4
+      go: 1.8.3
   - provider: s3
     access_key_id: AKIAIH2ZE2KZBNCVEGCA
     secret_access_key:
@@ -48,3 +49,4 @@ deploy:
     on:
       repo: wjdp/htmltest
       branch: master
+      go: 1.8.3