fix the syntax

appveyor.yml

@@ -1,8 +1,7 @@
 environment:
-  global:
-    matrix:
-      - TARGET=i686-pc-windows-msvc
-      - TARGET=x86_64-pc-windows-msvc
+  matrix:
+    - TARGET: i686-pc-windows-msvc
+    - TARGET: x86_64-pc-windows-msvc
 
 install:
   - ps: Start-FileDownload "https://static.rust-lang.org/dist/rust-nightly-${env:TARGET}.exe"