Fixed AppVeyor configuration to speed up the build process

* AppVeyor build only on 64 Bits OS

* Use the installed appveyor git
minor #64 Fixed AppVeyor configuration to speed up the build process (alquerci)

This PR was merged into the 1.1-dev branch.

Discussion
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| Q               | A
| --------------- | ---
| Bug fix?        | no
| New feature?    | no
| BC breaks?      | no
| Deprecations?   | no
| Tests pass?     | yes
| Related tickets | #38
| License         | GNU GPLv3

Commits
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8a3efe9 Fixed AppVeyor configuration to speed up the build process