updated Dart sample to align with best practices

lib/linguist/samples.json

@@ -527,7 +527,7 @@
       ".gemrc"
     ]
   },
-  "tokens_total": 439962,
+  "tokens_total": 439968,
   "languages_total": 515,
   "tokens": {
     "ABAP": {
@@ -15843,29 +15843,34 @@
       "return": 1
     },
     "Dart": {
+      "import": 1,
+      "as": 1,
+      "math": 1,
+      ";": 9,
       "class": 1,
-      "Point": 7,
+      "Point": 5,
       "{": 3,
+      "num": 2,
+      "x": 2,
+      "y": 2,
       "(": 7,
       "this.x": 1,
       "this.y": 1,
       ")": 7,
-      ";": 8,
       "distanceTo": 1,
       "other": 1,
-      "var": 3,
+      "var": 4,
       "dx": 3,
-      "x": 2,
       "-": 2,
       "other.x": 1,
       "dy": 3,
-      "y": 2,
       "other.y": 1,
       "return": 1,
-      "Math.sqrt": 1,
+      "math.sqrt": 1,
       "*": 2,
       "+": 1,
       "}": 3,
+      "void": 1,
       "main": 1,
       "p": 1,
       "new": 2,
@@ -47095,7 +47100,7 @@
     "Creole": 134,
     "CSS": 43867,
     "Cuda": 290,
-    "Dart": 68,
+    "Dart": 74,
     "Diff": 16,
     "DM": 169,
     "ECL": 281,
@@ -47350,5 +47355,5 @@
     "Xtend": 2,
     "YAML": 1
   },
-  "md5": "5703f25c45f067de03050cf5a2b5c401"
+  "md5": "d3bb6995f8f7fe57109f73fe079c19d2"
 }

samples/Dart/point.dart

@@ -1,15 +1,19 @@
+import 'dart:math' as math;
+
 class Point {
+  num x, y;
+
   Point(this.x, this.y);
-  distanceTo(Point other) {
+
+  num distanceTo(Point other) {
     var dx = x - other.x;
     var dy = y - other.y;
-    return Math.sqrt(dx * dx + dy * dy);
+    return math.sqrt(dx * dx + dy * dy);
   }
-  var x, y;
 }
 
-main() {
-  Point p = new Point(2, 3);
-  Point q = new Point(3, 4);
+void main() {
+  var p = new Point(2, 3);
+  var q = new Point(3, 4);
   print('distance from p to q = ${p.distanceTo(q)}');
 }