Update elm-reactor version in installation documentation

Ran into an installation issue that's described here: https://groups.google.com/forum/?fromgroups#!topic/elm-discuss/fsiDKEVSJXY The solution is to use elm-reactor-0.2.0.1 instead of 0.2.
Merge pull request #197 from stevenheidel/patch-1

Update elm-reactor version in installation documentation