Update rollup to the latest version 🚀

[greenkeeper]

The devDependency rollup was updated from 0.67.4 to 0.68.0.

This version is not covered by your current version range.

If you don’t accept this pull request, your project will work just like it did before. However, you might be missing out on a bunch of new features, fixes and/or performance improvements from the dependency update.

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[coveralls]

Pull Request Test Coverage Report for Build 204

• 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 100.0%

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Totals
Change from base Build 201:	0.0%
Covered Lines:	264
Relevant Lines:	264

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💛 - Coveralls

[greenkeeper]

• The devDependency rollup was updated from 0.67.4 to 0.68.1.

Update to this version instead 🚀

Release Notes for v0.68.1

2018-12-19

Bug Fixes

• Fix an issue with UMD wrappers where a variable is used without being defined (#2600)

Pull Requests

• #2600: Fix UMD and IIFE wrapper issues and add comprehensive functional wrapper tests (@lukastaegert)

Commits

The new version differs by 6 commits.

• 5516591 0.68.1
• 591692a Update changelog
• 8f71071 Fix UMD wrapper issues and refine wrappers (#2600)
• 7708970 Update changelog
• 824f942 Update changelog
• 790b270 Update changelog

See the full diff