Update dependencies, min Rust version to 1.25.0

crossbeam-utils needs Rust >= 1.25.0

.appveyor.yml

   - TARGET: x86_64-pc-windows-msvc
     CHANNEL: stable
   - TARGET: x86_64-pc-windows-msvc
-    CHANNEL: 1.24.1
+    CHANNEL: 1.25.0
   - TARGET: x86_64-pc-windows-gnu
     CHANNEL: stable
   - TARGET: x86_64-pc-windows-gnu

.travis.yml

   - stable
   - beta
   - nightly
-  - 1.24.0
+  - 1.25.0
 cache: cargo
 dist: trusty
 sudo: false