Merge pull request #141 from zishang520/patch-1

fix: GCJ02ToWGS84 accuracy

modules/transform/CoordTransform.js

     if (this.out_of_china(lng, lat)) {
       return [lng, lat]
     } else {
-      let d = this.delta(lng, lat)
-      let mgLng = lng + d[0]
-      let mgLat = lat + d[1]
-      return [lng * 2 - mgLng, lat * 2 - mgLat]
+      let out = [lng, lat]
+
+      let gcj02_point = this.WGS84ToGCJ02(lng, lat)
+      let dlng = gcj02_point[0] - lng
+      let dlat = gcj02_point[1] - lat
+      do {
+        gcj02_point = this.WGS84ToGCJ02((out[0] -= dlng), (out[1] -= dlat))
+        dlng = gcj02_point[0] - lng
+        dlat = gcj02_point[1] - lat
+      } while (Math.abs(dlng) > 1e-7 || Math.abs(dlat) > 1e-7)
+
+      return out
     }
   }