travis: fix build issue
travis: fix build issue

When building with Go 1.6, the build fails due to the missing "context"
package. Using Go 1.7 solves this issue.

Beside that, Terraform requires Go 1.7.

Signed-off-by: Thomas Hipp <ba262c2d62f6fd76f236e5802148840e86e9b719@suse.de>

dmacvicar/terraform-provider-libvirt,dmacvicar/terraform-provider-libvirt,flavio/terraform-provider-libvirt,deasmi/terraform-provider-libvirt,deasmi/terraform-provider-libvirt,deasmi/terraform-provider-libvirt,dmacvicar/terraform-provider-libvirt