Update Babel compiler toolchain to 7.0

Author: dgraham

.babelrc

@@ -2,21 +2,21 @@
   "env": {
     "esm": {
       "plugins": [
-        "transform-object-rest-spread",
+        "@babel/plugin-proposal-object-rest-spread",
         "transform-custom-element-classes"
       ],
       "presets": [
-        ["flow"],
-        ["es2015", {"modules": false}],
+        ["@babel/flow"],
+        ["@babel/env", {"modules": false}],
       ]
     },
     "umd": {
       "plugins": [
-        "transform-object-rest-spread",
+        "@babel/plugin-proposal-object-rest-spread",
         "transform-custom-element-classes",
-        "transform-es2015-modules-umd"
+        "@babel/plugin-transform-modules-umd"
       ],
-      "presets": ["flow", "es2015"]
+      "presets": ["@babel/flow", "@babel/env"]
     }
   }
 }