Remove polyfill, allow consumers to choose

Fixes #9

Author: OliverJAsh

package.json

@@ -56,8 +56,7 @@
     ]
   },
   "dependencies": {
-    "babel-plugin-transform-es2015-modules-commonjs": "6.24.1",
-    "intersection-observer": "^0.2.1"
+    "babel-plugin-transform-es2015-modules-commonjs": "6.24.1"
   },
   "peerDependencies": {
     "prop-types": "^15.5.10",

src/intersection.js

@@ -1,8 +1,3 @@
-if (global.window && !process.env.SERVER) {
-  // eslint-disable-next-line global-require
-  require('intersection-observer')
-}
-
 const INSTANCE_MAP = new Map()
 const OBSERVER_MAP = new Map()
 

yarn.lock

@@ -3138,10 +3138,6 @@ interpret@^1.0.0:
   version "1.0.3"
   resolved "https://registry.yarnpkg.com/interpret/-/interpret-1.0.3.tgz#cbc35c62eeee73f19ab7b10a801511401afc0f90"
 
-intersection-observer@^0.2.1:
-  version "0.2.1"
-  resolved "https://registry.yarnpkg.com/intersection-observer/-/intersection-observer-0.2.1.tgz#cb55175f4eebef6436d957a7d1774d39a9248e5e"
-
 invariant@2.x.x, invariant@^2.2.0, invariant@^2.2.2:
   version "2.2.2"
   resolved "https://registry.yarnpkg.com/invariant/-/invariant-2.2.2.tgz#9e1f56ac0acdb6bf303306f338be3b204ae60360"