Bump node-sass from 4.12.0 to 4.13.1

Sourced from node-sass's releases.

<h2>v4.13.1</h2> <h3>Community</h3>

• Fix render example syntax (@ZoranPandovski , #2787)
• Fix sourceMap option inconsistencies (@saper , #2394)
• Fix possible crash in customer importer (@xzyfer, #2816)

<h2>Supported Environments</h2>

OS	Architecture	Node
Windows	x86 & x64	0.10, 0.12, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13
OSX	x64	0.10, 0.12, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13
Linux*	x86 & x64	0.10, 0.12, 1, 2, 3, 4, 5, 6, 7, 8**, 9**, 10**^, 11**^, 12**^, 13**^
Alpine Linux	x64	6, 8, 10, 11, 12, 13
FreeBSD	i386 amd64	8, 10, 12, 13

*Linux support refers to Ubuntu, Debian, and CentOS 5+ ** Not available on CentOS 5 ^ Only available on x64

<h2>v4.13.0</h2> <h3>Features</h3>

• Node 13 support (@saper, #2766 #2767)

<h3>Community</h3>

• Fix broken link to NodeJS docs in README.md (@schwigri, #2753)
• Assorted typo fixes (@XhmikosR , #2726)
• Remove PR template (@nschonni)
• Remove sudo settings from .travis.yml (@abetomo, #2673)
• Add note in PR template about node-gyp 4.0 (@nschonni)
• Change note about Node 12 support (@nschonni)

<h3>Dependencies</h3>

• lodash@^4.17.15 (@kessenich, #2574)

<h2>Supported Environments</h2>

OS	Architecture	Node
Windows	x86 & x64	0.10, 0.12, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13
OSX	x64	0.10, 0.12, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13
Linux*	x86 & x64	0.10, 0.12, 1, 2, 3, 4, 5, 6, 7, 8**, 9**, 10**^, 11**^, 12**^, 13**^
Alpine Linux	x64	6, 8, 10, 11, 12, 13
FreeBSD	i386 amd64	6, 8, 10, 12, 13

*Linux support refers to Ubuntu, Debian, and CentOS 5+

Sourced from node-sass's changelog.

<h2>v4.13.1</h2>

https://github.com/sass/node-sass/releases/tag/v4.13.1

<h2>v4.13.0</h2>

https://github.com/sass/node-sass/releases/tag/v4.13.0

• 01db051 4.13.1
• 338fd7a Merge pull request from GHSA-f6rp-gv58-9cw3
• c6f2e5a doc: README example fix (#2787)
• fbc9ff5 Merge pull request #2754 from saper/no-map-if-not-requested
• 60fad5f 4.13.0
• 43db915 Merge pull request #2768 from sass/release-4-13
• 0c8d308 Update references for v4.13 release
• f1cc0d3 Use GCC 6 for Node 12 binaries (#2767)
• 3838eae Use GCC 6 for Node 12 binaries
• e84c6a9 Merge pull request #2766 from saper/node-modules-79
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