Update lru-cache to version 4.0.0 🚀

[greenkeeperio-bot]

Hello :wave:

:rocket::rocket::rocket:

lru-cache just published its new version 4.0.0, 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 lru-cache – 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 38 commits .

• da374d4 v4.0.0
• e76f4a0 feat(prune): allow users to proactively prune old entries
• f092bc4 doc: get() can return undefined
• f61b890 more timing bs in inspect test for travis's benefit
• 7ba1aaa wait longer for staleness in inspect test (failing on travis)
• 216f703 set vim nowrap on inspect test
• a39d90d remove memory test no longer relevant, and binary module breaks a lot
• 4e35642 update travis
• 3a6bcae upgrade to newer tap version
• 9fc38df ignore lcov coverage output folder
• 85517e3 Add custom inspect method
• 116a219 remove console.error in memory leak test
• f49f2da Use Symbols for private members
• 9edc4c0 remove overflow test, no longer relevant
• 790ba29 Add maxAge setter/getter, more tests for 100% cov

There are 38 commits in total. See the full diff.

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