Pub --trace suggestion is busted on Windows

[DartBot]

<img src="https://avatars.githubusercontent.com/u/188?v=3" align="left" width="96" height="96"hspace="10"> Issue by nex3
Originally opened as dart-lang/sdk#21843

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Currently if pub crashes, it suggests that users run "'pub' '--trace' ...". Single quotes work fine on Linux and Mac, but on Windows they're interpreted as part of the argument which breaks the invocation. We should suggest double quotes instead, which work across platforms.

[whesse]

Fixed in commit
2c051a1