set first coordinates instead of unshifting from the input

this ensures that the first point in a `LineString` isn't removed. fixes #9

src/geojson-tools.js

@@ -405,7 +405,7 @@ var complexify = function (linestring, distance) {
     result = [],
     points = [],
     d;
-  cur = linestring.shift();
+  cur = linestring[0];
   result.push(cur);
   points.push(cur);
   // variables used in the loop