Travis testing of Go changes

Use gimme to install a version of Go to test. Travis already uses gimme
to pre-install a version of Go.
Switch some of the Go testing from travis to xenial.

.travis.yml

@@ -31,14 +31,19 @@ matrix:
       dist: trusty
     - compiler: gcc
       os: linux
-      env: SWIGLANG=go
+      env: SWIGLANG=go VER=1.3
       sudo: required
-      dist: trusty
+      dist: xenial
     - compiler: gcc
       os: linux
-      env: SWIGLANG=go VER=1.5
+      env: SWIGLANG=go VER=1.8
       sudo: required
-      dist: trusty
+      dist: xenial
+    - compiler: gcc
+      os: linux
+      env: SWIGLANG=go VER=1.12
+      sudo: required
+      dist: xenial
     - compiler: gcc
       os: linux
       env: SWIGLANG=guile

Tools/travis-linux-install.sh

@@ -37,6 +37,9 @@ case "$SWIGLANG" in
 		travis_retry sudo dpkg -i dmd_2.066.0-0_amd64.deb
 		;;
 	"go")
+		if [[ "$VER" ]]; then
+		  eval "$(gimme ${VER}.x)"
+		fi
 		;;
 	"javascript")
 		case "$ENGINE" in