Fix appveyor.yml

Author: lukebakken

appveyor.yml

@@ -14,8 +14,8 @@ environment:
 cache:
   # Note: this must match the $rabbitmq_installer_path and $erlang_installer_path values in
   # tools\appveyor\install.ps1
-  - "%HOMEDRIVE%%HOMEPATH%\rabbitmq-server-3.8.2.exe"
-  - "%HOMEDRIVE%%HOMEPATH%\otp_win64_22.2.exe"
+  - "%HOMEDRIVE%%HOMEPATH%\\rabbitmq-server-3.8.2.exe"
+  - "%HOMEDRIVE%%HOMEPATH%\\otp_win64_22.2.exe"
 
 install:
   - IF DEFINED SNKSECRET (nuget install secure-file -ExcludeVersion)