Change try-build CI-image for testing purporses.

Author: michaelwoerister

.travis.yml

@@ -19,7 +19,7 @@ matrix:
     - env: IMAGE=x86_64-gnu-llvm-6.0 RUST_BACKTRACE=1
       if: type = pull_request OR branch = auto
 
-    - env: IMAGE=dist-x86_64-linux DEPLOY=1
+    - env: IMAGE=x86_64-gnu-debug
       if: branch = try OR branch = auto
 
     # "alternate" deployments, these are "nightlies" but have LLVM assertions