Update to React 15.6

Once we're upgraded to React 15.x and have no deprecation warnings,
upgrading to React 16 should be painless.

PureRenderMixin has been superceded by PureComponent. According to the
docs PureComponent should only be used if all of it's children are also
"pure".

https://facebook.github.io/react/docs/react-api.html#react.purecomponent

app/scripts/views/pie_chart.js

@@ -1,15 +1,13 @@
 import Chartist from "Chartist";
-import React, { Component } from "react";
-import PureRenderMixin from "react-addons-pure-render-mixin";
+import React, { PureComponent } from "react";
 
-export default class LevelView extends Component {
+export default class LevelView extends PureComponent {
   static propTypes = {
     pieParts: React.PropTypes.array.isRequired
   };
 
   constructor(props, context) {
     super(props, context);
-    this.shouldComponentUpdate = PureRenderMixin.shouldComponentUpdate.bind(this);
   }
 
   render() {

app/scripts/views/rhythm_settings_view.js

@@ -1,5 +1,4 @@
 import React, { Component } from "react";
-import PureRenderMixin from "react-addons-pure-render-mixin";
 import RangeSettingComponent from "./range_setting_component";
 import SettingLine from "./setting_line";
 import AnalyticsService from "../services/analytics_service.js";
@@ -12,7 +11,6 @@ export default class PitchSettingsView extends Component {
 
   constructor(props, context) {
     super(props, context);
-    this.shouldComponentUpdate = PureRenderMixin.shouldComponentUpdate.bind(this);
   }
 
   buildStateChanger(stateKey) {

app/scripts/views/rhythm_statistic_view.js

@@ -5,7 +5,6 @@ import _ from "lodash";
 
 import AnimatedNumber from "./animated_number.js";
 import StarAnimation from "./star_animation.js";
-import PureRenderMixin from "react-addons-pure-render-mixin";
 
 export default class RhythmStatisticView extends Component {
   static propTypes = {
@@ -14,7 +13,6 @@ export default class RhythmStatisticView extends Component {
 
   constructor(props) {
     super(props);
-    this.shouldComponentUpdate = PureRenderMixin.shouldComponentUpdate.bind(this);
   }
 
   getHumanReadableTime(milliseconds) {

app/scripts/views/stave_renderer.js

@@ -1,23 +1,21 @@
 import Vex from "vexflow";
-import React, { Component } from "react";
+import React, { PureComponent } from "react";
 import _ from "lodash";
-import PureRenderMixin from "react-addons-pure-render-mixin";
 
-class StaveRenderer extends Component {
+class StaveRenderer extends PureComponent {
   static defaultProps = {
     staveCount: 2
   };
 
   static propTypes = {
-    keys: React.PropTypes.array,
+    keys: React.PropTypes.objectOf(React.PropTypes.array),
     chordIndex: React.PropTypes.number,
     keySignature: React.PropTypes.string,
     staveCount: React.PropTypes.number
   };
 
   constructor(props) {
     super(props);
-    this.shouldComponentUpdate = PureRenderMixin.shouldComponentUpdate.bind(this);
   }
 
   render() {

package.json

@@ -21,10 +21,9 @@
     "freezer-js": "git+https://github.com/philippotto/freezer.git#native-object-handling-build",
     "html-loader": "^0.4.3",
     "lodash": "^4.5.1",
-    "react": "^0.14.5",
-    "react-addons-pure-render-mixin": "^0.14.8",
+    "react": "^15.6.1",
     "react-bootstrap": "^0.28.3",
-    "react-dom": "^0.14.5",
+    "react-dom": "^15.6.1",
     "react-motion": "^0.4.2",
     "react-range-slider-bem": "^0.2.11",
     "vexflow": "^1.2.41"