About TypeScript 2.3 --checkJs

Please consider supporting Type Checking JavaScript Files

[cancerberoSgx]

Since typescript supports jsdoc - closure annotations this feature sis very important for those of us that cannot migrate to typescript and must continue working in vanilla javascript. Please Please so support --checkJs and --allowJs. Thanks

[felixfbecker]

@cancerberoSgx this depends on updating to the latest TypeScript version - feel free to take #379 or #385 over the finish line

[felixfbecker]

Actually, we already use TS 2.4. So this should work.