Drop babel-runtime

Fixes #243.

.babelrc

@@ -1,20 +1,33 @@
 {
-  "plugins": [
-    "transform-runtime"
-  ],
   "env": {
     "test": {
       "presets": [
-        [ "env", { "loose": true, "targets": { "node": 4 } } ]
+        [ "env", {
+	  "loose": true,
+	  "targets": { "node": 4 },
+	  "exclude": [
+	    // skip some almost-compliant features on Node.js v4.x
+	    "transform-es2015-block-scoping",
+	    "transform-es2015-classes",
+	    "transform-es2015-for-of",
+	  ]
+	} ]
       ],
       "plugins": [
-        "transform-runtime",
 	"./build/babel-plugin"
       ]
     },
     "coverage": {
       "presets": [
-        [ "env", { "loose": true, "targets": { "node": 4 } } ]
+        [ "env", {
+	  "loose": true,
+	  "targets": { "node": 4 },
+	  "exclude": [
+	    "transform-es2015-block-scoping",
+	    "transform-es2015-classes",
+	    "transform-es2015-for-of"
+	  ]
+	} ]
       ],
       "plugins": [
         [ "istanbul", { "exclude": [ "src/blob.js", "build", "test" ] } ],
@@ -23,7 +36,16 @@
     },
     "rollup": {
       "presets": [
-        [ "env", { "loose": true, "targets": { "node": 4 }, "modules": false } ]
+        [ "env", {
+	  "loose": true,
+	  "targets": { "node": 4 },
+	  "exclude": [
+	    "transform-es2015-block-scoping",
+	    "transform-es2015-classes",
+	    "transform-es2015-for-of"
+	  ],
+	  "modules": false
+	} ]
       ]
     }
   }

package.json

@@ -56,7 +56,6 @@
     "whatwg-url": "^4.0.0"
   },
   "dependencies": {
-    "babel-runtime": "^6.11.6",
     "encoding": "^0.1.11"
   }
 }