Release 2.3.1

• build: upgrade CI build to node 12 (b879b7d)
• Merge pull request #134 from ShabadOS/subscript-support (88476b4)
• refactor(toEnglish): remove explicit passthrough list in favour of passthrough by default (a497a4a)
• fix(toEnglish): add passthrough for letters that are not in the transliteration map (b256c3e)
• build: move pre-commit hook to correct hooks section in package.json (f6443de)
• build(deps-dev): bump release-it from 12.4.3 to 13.1.1 (8f8cea4)
• build: upgrade husky pre-commit hook in package.json (c2dfc2e)
• build(deps-dev): bump husky from 0.14.3 to 4.2.3 (2bc4e05)
• build(deps): [security] bump acorn from 6.1.0 to 6.4.1 (33e3121)
• build(deps-dev): bump mocha from 5.2.0 to 7.1.1 (5f862be)
• build(deps-dev): bump eslint-plugin-import from 2.19.1 to 2.20.1 (cf480cd)
• build(deps-dev): bump eslint-plugin-react from 7.17.0 to 7.18.3 (21b2c38)
• build(deps-dev): bump nyc from 14.1.1 to 15.0.0 (92a523e)
• [Security] Bump tar from 4.4.1 to 4.4.10 (6d6bbf7)
• [Security] Bump lodash.template from 4.4.0 to 4.5.0 (38f634a)
• Bump escape-string-regexp from 1.0.5 to 2.0.0 (e454bed)