fixed typo (#32)

tk3369 · joshday · commit 1a37863fab04 · 2019-06-05T11:31:10.000-04:00
diff --git a/src/LearnBase.jl b/src/LearnBase.jl
@@ -331,7 +331,7 @@ Singleton types to define which dimension of some data structure
 
 - `ObsDim.First()`
 - `ObsDim.Last()`
-- `ObsDim.Contant(dim)`
+- `ObsDim.Constant(dim)`
 
 Used for efficient dispatching
 """
