Fix typo in description of convertFarenheitToCelsius() (#222)

This typo came from ac5ce6a.

Author: amartini51

TSPL.docc/LanguageGuide/Concurrency.md

@@ -1113,7 +1113,7 @@ while unit conversion is in progress.
 In addition to writing code in an actor
 that protects temporary invalid state by omitting potential suspension points,
 you can move that code into a synchronous method.
-The `convertFarenheitToCelsius()` method above is method,
+The `convertFarenheitToCelsius()` method above is a synchronous method,
 so it's guaranteed to *never* contain potential suspension points.
 This function encapsulates the code
 that temporarily makes the data model inconsistent,