Updated rust version to 1.11.0 in appveyor script

Author: Pierre-Henri Symoneaux

appveyor.yml

@@ -1,6 +1,6 @@
 install:
-  - ps: Start-FileDownload 'https://static.rust-lang.org/dist/rust-1.10.0-x86_64-pc-windows-gnu.exe'
-  - rust-1.10.0-x86_64-pc-windows-gnu.exe /VERYSILENT /NORESTART /DIR="C:\Program Files (x86)\Rust"
+  - ps: Start-FileDownload 'https://static.rust-lang.org/dist/rust-1.11.0-x86_64-pc-windows-gnu.exe'
+  - rust-1.11.0-x86_64-pc-windows-gnu.exe /VERYSILENT /NORESTART /DIR="C:\Program Files (x86)\Rust"
   - SET PATH=%PATH%;C:\Program Files (x86)\Rust\bin
   - rustc -V
   - cargo -V