Officially drop IE9-10 support, pull out our hacks (#2296)

- I also fixed a bunch of related comments
- I had to polyfill `requestAnimationFrame` for Node
- Drive-by: run `eslint . --fix`
- Drive-by: update transpiling info in CONTRIBUTING.md
- Drive-by: we aren't the only ones going semicolon-free

request/tests/test-request.js

@@ -415,9 +415,9 @@ o.spec("xhr", function() {
 			xhr({method: "GET", url: "/item", config: handleAbort}).catch(function() {
 				failed = true
 			})
-			.then(function() {
-				resolved = true
-			})
+				.then(function() {
+					resolved = true
+				})
 		})
 		o("doesn't fail on file:// status 0", function(done) {
 			mock.$defineRoutes({