CI: use Miniconda3 and Python 3.7 for travis build

Save resources and only test scons build with Python 2.7 on Linux.

Author: pavoljuhas

.travis.yml

@@ -8,10 +8,14 @@ os:
 
 env:
   - MYUSEMC=true MYPYTHON_VERSION=2.7
-  - MYUSEMC=true MYPYTHON_VERSION=3.5
-  - MYUSEMC=true MYPYTHON_VERSION=3.6
+  - MYUSEMC=true MYPYTHON_VERSION=3.7
   - MYUSEMC=false
 
+matrix:
+  exclude:
+    - os: osx
+      env: MYUSEMC=true MYPYTHON_VERSION=2.7
+
 git:
   depth: 999999
 
@@ -40,9 +44,9 @@ before_install:
   - MYMCREPO=https://repo.continuum.io/miniconda
   - case ${TRAVIS_OS_NAME} in
     linux)
-        MYMCBUNDLE=Miniconda2-latest-Linux-x86_64.sh ;;
+        MYMCBUNDLE=Miniconda3-latest-Linux-x86_64.sh ;;
     osx)
-        MYMCBUNDLE=Miniconda2-latest-MacOSX-x86_64.sh ;;
+        MYMCBUNDLE=Miniconda3-latest-MacOSX-x86_64.sh ;;
     *)
         echo "Unsupported operating system." >&2;
         exit 2 ;;