Fix misspelled "across"

Author: nikai3d

examples/sorting-by-functions/sorting-by-functions.go

@@ -18,7 +18,7 @@ type ByLength []string
 // We implement `sort.Interface` - `Len`, `Less`, and
 // `Swap` - on our type so we can use the `sort` package's
 // generic `Sort` function. `Len` and `Swap`
-// will usually be similar accross types and `Less` will
+// will usually be similar across types and `Less` will
 // hold the actual custom sorting logic. In our case we
 // want to sort in order of increasing string length, so
 // we use `len(s[i])` and `len(s[j])` here.