Update systemjs-builder to version 0.15.18 🚀

[greenkeeperio-bot]

Hello :wave:

:rocket::rocket::rocket:

systemjs-builder just published its new version 0.15.18, which is not covered by your current version range.

If this pull request passes your tests you can publish your software with the latest version of systemjs-builder – otherwise use this branch to work on adaptions and fixes.

Happy fixing and merging :palm_tree:

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The new version differs by 508 commits .

• 271934f 0.15.18
• 430e99a source map extraction to only use // comments, node 6 support
• 0164594 use pluginloader for plugin canonicalization
• 5417f46 note on environment paths
• e78f0e6 ensure fetch is called with Promise.resolve
• b6c5e3d 0.15.17
• f8d8563 System.register metadata.deps support note
• 3378663 recursive map config fix
• 61d7540 fetch default hook to include caching
• 8316062 rollup sourcemaps sources correction, handle sanitization entirely in loader
• 1a25fd0 Merge pull request #568 from asapach/master
• 1228897 added support for input source maps
• 5dae1e9 update source maps expectations
• 6ba5476 source maps debugging
• a4fd3ec template minification

There are 250 commits in total. See the full diff.

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