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.
diff --git a/.travis.yml b/.travis.yml
index 78d8883..61021b4 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -31,14 +31,19 @@
       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
diff --git a/Tools/travis-linux-install.sh b/Tools/travis-linux-install.sh
index dc85265..bfa7bf8 100755
--- a/Tools/travis-linux-install.sh
+++ b/Tools/travis-linux-install.sh
@@ -37,6 +37,9 @@
 		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