Gardening: fix comment typo in build_swift/migration.py

Author: MaxDesiatov

utils/build_swift/build_swift/migration.py

@@ -8,7 +8,7 @@
 
 
 """
-Temporary module with functionaly used to migrate away from build-script-impl.
+Temporary module with functionality used to migrate away from build-script-impl.
 """