Disable CI on non nightlies

Currently the feature(alloc_system) prevents us from
building on stable and beta

The tracking issue is here:
rust-lang/rust#33082

.appveyor.yml

@@ -4,17 +4,17 @@ environment:
   matrix:
 ### MSVC Toolchains ###
   # Stable 64-bit MSVC
-    - channel: stable
-      target: x86_64-pc-windows-msvc
+  #  - channel: stable
+  #    target: x86_64-pc-windows-msvc
   # Stable 32-bit MSVC
-    - channel: stable
-      target: i686-pc-windows-msvc
+  #  - channel: stable
+  #    target: i686-pc-windows-msvc
   # Beta 64-bit MSVC
-    - channel: beta
-      target: x86_64-pc-windows-msvc
+  #  - channel: beta
+  #    target: x86_64-pc-windows-msvc
   # Beta 32-bit MSVC
-    - channel: beta
-      target: i686-pc-windows-msvc
+  #  - channel: beta
+  #    target: i686-pc-windows-msvc
   # Nightly 64-bit MSVC
     - channel: nightly
       target: x86_64-pc-windows-msvc
@@ -26,17 +26,17 @@ environment:
 
 ### GNU Toolchains ###
   # Stable 64-bit GNU
-    - channel: stable
-      target: x86_64-pc-windows-gnu
+  #- channel: stable
+  #   target: x86_64-pc-windows-gnu
   # Stable 32-bit GNU
-    - channel: stable
-      target: i686-pc-windows-gnu
+  #  - channel: stable
+  #    target: i686-pc-windows-gnu
   # Beta 64-bit GNU
-    - channel: beta
-      target: x86_64-pc-windows-gnu
+  #  - channel: beta
+  #    target: x86_64-pc-windows-gnu
   # Beta 32-bit GNU
-    - channel: beta
-      target: i686-pc-windows-gnu
+  #  - channel: beta
+  #    target: i686-pc-windows-gnu
   # Nightly 64-bit GNU
     - channel: nightly
       target: x86_64-pc-windows-gnu

.travis.yml

@@ -1,6 +1,14 @@
 language: rust
 sudo: false
 
+os:
+  - linux
+  - osx
+rust:
+  - nightly
+  #- beta
+  #- stable
+
 addons:
   apt:
     packages:
@@ -14,20 +22,6 @@ addons:
 
 matrix:
   fast_finish: true
-  include:
-    - os: linux
-      rust: nightly
-    - os: linux
-      rust: beta
-    - os: linux
-      rust: stable
-
-    - os: osx
-      rust: nightly
-    - os: osx
-      rust: beta
-    - os: osx
-      rust: stable
 
 script:
   - (cd dbgp && cargo build --verbose)