放宽引用gist的格式

[xiaket]

讨论参见: http://www.v2ex.com/t/74249

print gist("http://gist.github.com/123078.git")
<script src="http://gist.github.com/123078.js"></script>
print gist("http://gist.github.com/123078")
<script src="http://gist.github.com/123078.js"></script>
print gist("https://gist.github.com/123078")
<script src="https://gist.github.com/123078.js"></script>
print gist("https://gist.github.com/123078.git")
<script src="https://gist.github.com/123078.js"></script>

[livid]

Thanks!

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