Use v2_48 as highest version because that's what outdated Travis has

This should be reverted once someone figured out how to actually test
something in a meaningful way on Travis.

Author: sdroege

.travis.yml

@@ -7,43 +7,43 @@ matrix:
       env: GTK=3.14 FEATURES=subclassing
     - os: linux
       rust: nightly
-      env: GTK=3.24 FEATURES=subclassing,v2_58
+      env: GTK=3.24 FEATURES=subclassing,v2_48
     - os: linux
       rust: beta
       env: GTK=3.14 FEATURES=subclassing
     - os: linux
       rust: beta
-      env: GTK=3.24 FEATURES=subclassing,v2_58
+      env: GTK=3.24 FEATURES=subclassing,v2_48
     - os: linux
       rust: 1.31.0
       env: GTK=3.14 FEATURES=subclassing
     - os: linux
       rust: 1.31.0
-      env: GTK=3.24 FEATURES=subclassing,v2_58
+      env: GTK=3.24 FEATURES=subclassing,v2_48
     - os: osx
       rust: nightly
       env: GTK=3.14 FEATURES=subclassing
     # - os: osx
     #   rust: nightly
-    #   env: GTK=3.24 FEATURES=subclassing,v2_58
+    #   env: GTK=3.24 FEATURES=subclassing,v2_48
     - os: osx
       rust: beta
       env: GTK=3.14 FEATURES=subclassing
     # - os: osx
     #   rust: beta
-    #   env: GTK=3.24 FEATURES=subclassing,v2_58
+    #   env: GTK=3.24 FEATURES=subclassing,v2_48
     - os: osx
       rust: stable
       env: GTK=3.14 FEATURES=subclassing
     # - os: osx
     #   rust: stable
-    #   env: GTK=3.24 FEATURES=subclassing,v2_58
+    #   env: GTK=3.24 FEATURES=subclassing,v2_48
     - os: linux
       rust: nightly
       env: GTK=3.14 FEATURES=subclassing ARM=1 OTHER_TARGET="--target armv7-unknown-linux-gnueabihf"
     - os: linux
       rust: nightly
-      env: GTK=3.24 FEATURES=subclassing,v2_58 ARM=1 OTHER_TARGET="--target armv7-unknown-linux-gnueabihf"
+      env: GTK=3.24 FEATURES=subclassing,v2_48 ARM=1 OTHER_TARGET="--target armv7-unknown-linux-gnueabihf"
 addons:
   apt:
     packages: