Adding a missing isosceles case
Adding a missing isosceles case

pointed out by @plinto in http://exercism.io/submissions/1a614864d2dc44bdb18e1be9f5f6970e
marcCanipel/xjavascript,cloudleo/xjavascript,marcCanipel/xjavascript,cloudleo/xjavascript,exercism/xjavascript,exercism/xjavascript