Remove old Ruby versions from CI config & cross compile rake task

Author: aharpervc

.travis.yml

@@ -8,7 +8,6 @@ env:
     - TESTOPTS="-v"
     - TINYTDS_UNIT_HOST=localhost
 rvm:
-  - 2.3.8
   - 2.4.5
   - 2.5.3
   - 2.6.1

tasks/native_gem.rake

@@ -8,7 +8,7 @@ task 'gem:windows' => ['ports:cross'] do
   build = ['bundle']
 
   # and finally build the native gem
-  build << 'rake cross native gem RUBY_CC_VERSION=2.5.0:2.4.0:2.3.0:2.2.2:2.1.6:2.0.0 CFLAGS="-Wall" MAKE="make -j`nproc`"'
+  build << 'rake cross native gem RUBY_CC_VERSION=2.5.0:2.4.0 CFLAGS="-Wall" MAKE="make -j`nproc`"'
 
   RakeCompilerDock.sh build.join(' && ')
 end