Remove requirement to pass x-axis range explicitly

[henrygarner]

When (c/histogram data) is called without further arguments we get the following error:

Uncaught Error: nth not supported on this type function Boolean() { [native code] }
cljs.core.nth.cljs$core$IFn$_invoke$arity$3 @ core.cljs:1559
cljs$core$nth @ core.cljs:1498b1$layout$histogram$fixed_size_bins @ histogram.cljc?rel=1435855110581:25
b1.layout.histogram.histogram.cljs$core$IFn$_invoke$arity$variadic @ histogram.cljc?rel=1435855110581:64
b1$layout$histogram$histogram @ histogram.cljc?rel=1435855110581:32
b1.charts.histogram.cljs$core$IFn$_invoke$arity$variadic @ charts.cljc?rel=1435855110613:8
b1$charts$histogram @ charts.cljc?rel=1435855110613:6

Adding (c/histogram data :x-axis [0 1]) works around the problem for now.