Update league/flysystem from 1.0.46 to 1.0.47

[violinist-bot]

If you have a decent test suite, and your tests pass, it should be both safe and smart to merge this update.

Here is a list of changes between the version you use, and the version this pull request updates to:

• a11e4a7 increased visibility for extension mime type map
• 19feb1d Corrected epub mimetype map key
• cfdae1f Pre-release changelog
• faf30fd Fixes #964: specify mime-type for epub files
• 9386fec Require the fileinfo extension ad non-dev
• 23a0b48 Merge pull request #959 from phil-davis/minor-doc-edits-20180826
• d202d53 Minor doc edits

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