Bump the minimum Rust version to 1.30.1, following Cranelift's policy.

.travis.yml

@@ -2,9 +2,7 @@
 
 language: rust
 rust:
-    - stable
-    # The version of rust in the latest Ubuntu LTS, currently Bionic.
-    - 1.25.0
+    - 1.30.1
     - beta
     - nightly
 matrix:
@@ -13,6 +11,9 @@ matrix:
         # fail, so we don't allow them to hold up people using stable.
         - rust: beta
         - rust: nightly
+    # Similarly, we don't need to hold up people using stable while we wait
+    # for the results which may fail.
+    fast_finish: true
 dist: trusty
 sudo: false
 before_script: