Remove global side-effect

[rowanwins]

Hi @mfogel

We've been having a bit of trouble over at TurfJS with tree-shaking and we've been hunting a few spots where globals are being overridden.

Hopefully this PR is fairly straight-forward but let me know if you've got any questions.

Cheers
Rowan

[coveralls]

Pull Request Test Coverage Report for Build 216

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.002%) to 97.78%

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Totals
Change from base Build 215:	0.002%
Covered Lines:	645
Relevant Lines:	651

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 216

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.002%) to 97.78%

---

Totals
Change from base Build 215:	0.002%
Covered Lines:	645
Relevant Lines:	651

---

💛 - Coveralls

[mfogel]

@rowanwins thanks for the contribution

Let me know if there's other things that would make the integration with turfJS smoother/easier, happy to help out.

[rowanwins]

If you could publish that change to npm that would be fab thanks @mfogel

[mfogel]

sure - I'll try to push out a new release this weekend.

[mfogel]

@rowanwins new release v0.9.2 with this change is live on npm now. cheers!