• VSCode Version:0.10.13 alpha
• OS Version:Windows 10

Steps to Reproduce:

1. Add an variable to your tasks.json ex. ${env.PATH}
   "command": "echo",
   "isShellCommand": true,
   "args": ["${env.PATH}"],
2. Run the task.
   This will expand correctly on Linux and OS X but not Windows since the expansion is case sensitive and PATH on Windows is "Path".
   Env Var expansion shouldn't be case sensitive so that the same task can run on all platform.
   This bug was requested by @dbaeumer in vscode-docs issue tasks.json documentation innacurate? vscode-docs#247