Convert to TypeScript (TroyAlford#135)

Fixes TroyAlford#135 
* Convert all .js to .ts - and update build
* Bump version number
* Update Node version for builds on CircleCI
* Update test coverage & test coverage reporting

Author: TroyAlford

.babelrc

@@ -4,7 +4,8 @@
   ],
   "presets": [
     "@babel/preset-env",
-    "@babel/preset-react"
+    "@babel/preset-react",
+    "@babel/preset-typescript"
   ],
   "highlightCode": true
 }

.circleci/config.yml

@@ -3,7 +3,7 @@ jobs:
   build:
     working_directory: ~/react-jsx-parser
     docker:
-      - image: circleci/node:11.10.1
+      - image: circleci/node:12.9.1
     steps:
       - checkout
       - restore_cache:
@@ -17,7 +17,7 @@ jobs:
   test:
     working_directory: ~/react-jsx-parser
     docker:
-      - image: circleci/node:11.10.1
+      - image: circleci/node:12.9.1
     steps:
       - checkout
       - restore_cache: