fix(slice docs): slice_sample(n=5)

The docs have `slice_sample(5)` which only creates one sample (not 5).  Perhaps this is a code issue and not a doc issue.

Author: GlenHertz

docs/examples/UserGuide/slice.jl

@@ -64,7 +64,7 @@ end
 # ## Sample 5 random rows in the data frame
 
 @chain df begin
-  @slice_sample(5)
+  @slice_sample(n=5)
 end
 
 # ## Slice the min
@@ -99,4 +99,4 @@ end
 
 @chain df begin 
   @slice_head(n = 3)
-end
+end