Update mixin-deep to 1.3.2

Update mixin-deep from 1.3.1 to 1.3.2 to address a Prototype Pollution vulnerability, which exists in mixin-deep package, versions >=2.0.0 <2.0.1 || <1.3.2 (CVE-2019-10746).

• from: https://www.npmjs.com/package/mixin-deep/v/1.3.1
• to: https://www.npmjs.com/package/mixin-deep/v/1.3.2
• 2 commits (github.com): https://github.com/jonschlinkert/mixin-deep/compare/1.3.1...1.3.2
• Synk ID: https://app.snyk.io/vuln/SNYK-JS-MIXINDEEP-450212