Environment

• Editor and Version (VS Code, Atom, Sublime): VS Code 1.29.0
• Your primary theme: Dark+ (default dark)

Issue Description

Double-quoted strings color @tokens the same as $tokens

Screenshots

Expected Behavior

Only $tokens or $(expressions) are string-interpolated in a double-quoted string. The @word is just going to be treated as part of the string.

Code Samples

This may be an appropriate spec test case:

    "This is a @double quoted string."
#   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ string.quoted.double.powershell