[gardening] Fix recently introduced typo: "becasue" → "because"

Author: practicalswift

docs/StdlibRationales.rst

@@ -167,7 +167,7 @@ for it.
 
 Note that neither of the two ``sorted()`` methods (neither one that accepts a
 custom comparator closure, nor one that uses the ``Comparable`` conformace)
-can't be lazy, becasue the lazy version would be less efficient than the eager
+can't be lazy, because the lazy version would be less efficient than the eager
 one.
 
 A different design that was rejected is to preserve consistency with other