Remove version pinning from appveyor config
Remove version pinning from appveyor config

Summary:
Refs: https://github.com/facebook/watchman/issues/423

This pinning was added because newer versions failed to install.

http://help.appveyor.com/discussions/problems/5616-not-able-to-build-due-to-problem-in-chocolateyinstallps1#comment_41337217

suggests adding the `-i` flag to ignore deps, which is what we needed here to prevent the deps of php wanting to reboot the appveyor environment.
Closes https://github.com/facebook/watchman/pull/424

Differential Revision: D4425805

Pulled By: wez

fbshipit-source-id: ee3efec74a26bf86702603884d727b0730d68a2a

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