Translate contributors graph x-axis

app/assets/javascripts/graphs/stat_graph_contributors_graph.js

 /* eslint-disable func-names, space-before-function-paren, no-var, prefer-rest-params, max-len, no-restricted-syntax, vars-on-top, no-use-before-define, no-param-reassign, new-cap, no-underscore-dangle, wrap-iife, comma-dangle, no-return-assign, prefer-arrow-callback, quotes, prefer-template, newline-per-chained-call, no-else-return, no-shadow */
 import _ from 'underscore';
 import d3 from 'd3';
+import { createDateTimeFormat } from '../locale';
 
 const extend = function(child, parent) { for (var key in parent) { if (hasProp.call(parent, key)) child[key] = parent[key]; } function ctor() { this.constructor = child; } ctor.prototype = parent.prototype; child.prototype = new ctor(); child.__super__ = parent.prototype; return child; };
 const hasProp = {}.hasOwnProperty;
 
+const dayFormat = createDateTimeFormat({ month: 'short', day: 'numeric' });
+const monthFormat = createDateTimeFormat({ month: 'long' });
+const yearFormat = createDateTimeFormat({ year: 'numeric' });
+
+const xTickFormat = (date) => {
+  if (date.getDate() !== 1) {
+    return dayFormat.format(date);
+  } else if (date.getMonth() > 0) {
+    return monthFormat.format(date);
+  } else {
+    return yearFormat.format(date);
+  }
+};
+
 export const ContributorsGraph = (function() {
   function ContributorsGraph() {}
 
@@ -131,7 +146,10 @@ export const ContributorsMasterGraph = (function(superClass) {
   };
 
   ContributorsMasterGraph.prototype.create_axes = function() {
-    this.x_axis = d3.svg.axis().scale(this.x).orient("bottom");
+    this.x_axis = d3.svg.axis()
+      .scale(this.x)
+      .orient('bottom')
+      .tickFormat(xTickFormat);
     return this.y_axis = d3.svg.axis().scale(this.y).orient("left").ticks(5);
   };
 
@@ -219,7 +237,11 @@ export const ContributorsAuthorGraph = (function(superClass) {
   };
 
   ContributorsAuthorGraph.prototype.create_axes = function() {
-    this.x_axis = d3.svg.axis().scale(this.x).orient("bottom").ticks(8);
+    this.x_axis = d3.svg.axis()
+      .scale(this.x)
+      .orient('bottom')
+      .ticks(8)
+      .tickFormat(xTickFormat);
     return this.y_axis = d3.svg.axis().scale(this.y).orient("left").ticks(5);
   };