use the current Go 1.9 and 1.10 versions on Travis

.travis.yml

 language: go
 
 go:
-  - 1.9
+  - "1.9.x"
+  - "1.10.x"
 
 # first part of the GOARCH workaround
 # setting the GOARCH directly doesn't work, since the value will be overwritten later