build: Some minor improvements to appveyor

* Add cache support
* Finish all build jobs if one failed

Author: tesuji

appveyor.yml

@@ -12,17 +12,16 @@ cache:
   - target
 
 environment:
-  global:
-    RUSTFLAGS: -Ctarget-feature=+crt-static
-    RUST_BACKTRACE: 1
+  RUSTFLAGS: -Ctarget-feature=+crt-static
+  RUST_BACKTRACE: 1
   matrix:
     fast_finish: true
-    - TARGET: x86_64-pc-windows-msvc
-      NO_ADD: 1
-      ALLOW_PR: 1
-    - TARGET: i686-pc-windows-msvc
-    access_token:
-      secure: q8Wqx0brgfpOYFQqWauvucE2h0o1WYb41a3gKaCKV9QiE4eTz6qLNlqyC3mdsp4Q
+  - TARGET: x86_64-pc-windows-msvc
+    NO_ADD: 1
+    ALLOW_PR: 1
+  - TARGET: i686-pc-windows-msvc
+  access_token:
+    secure: q8Wqx0brgfpOYFQqWauvucE2h0o1WYb41a3gKaCKV9QiE4eTz6qLNlqyC3mdsp4Q
 
 install:
   # If this is a PR and we're not allowed to test PRs, skip the whole build.