SkyView: Fix trail color for planes that are now on ground

When determining the color for a given altitude, don't check the current
altitude if it's ground but the altitude passed as an argument to the
function.
Without this fix, when clicking an aircraft on ground, its entire trail
is drawn in the color for ground.

public_html/planeObject.js

@@ -337,7 +337,7 @@ PlaneObject.prototype.getAltitudeColor = function(altitude) {
                 h = ColorByAlt.unknown.h;
                 s = ColorByAlt.unknown.s;
                 l = ColorByAlt.unknown.l;
-        } else if (this.altitude === "ground") {
+        } else if (altitude === "ground") {
                 h = ColorByAlt.ground.h;
                 s = ColorByAlt.ground.s;
                 l = ColorByAlt.ground.l;