Add missing import. Fixes #31

[Xarthisius]

Fetch transport for globus was missing an import.

fetch_globus.py:76:23: F821 undefined name 'ensure_valid_output_path'

[coveralls]

Pull Request Test Coverage Report for Build 246

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 92.588%

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Totals
Change from base Build 244:	0.0%
Covered Lines:	1449
Relevant Lines:	1565

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💛 - Coveralls

[mikedarcy]

Oops. Sorry about this. It would have been caught if there were better unit tests for Globus Transfer. Those are problematic because of all of the machinery involved. However, I will look into doing some mock invocations into the module which certainly would have caught an import issue like this one.