spelling: availability

Signed-off-by: Josh Soref <jsoref@users.noreply.github.com>

Author: jsoref

utils/gyb_syntax_support/StmtNodes.py

@@ -197,8 +197,8 @@
              Child('Condition', kind='Syntax',
                    node_choices=[
                        Child('Expression', kind='Expr'),
-                       Child('Availablity', kind='AvailabilityCondition'),
-                       Child('Unavailablity', kind='UnavailabilityCondition'),
+                       Child('Availability', kind='AvailabilityCondition'),
+                       Child('Unavailability', kind='UnavailabilityCondition'),
                        Child('MatchingPattern',
                              kind='MatchingPatternCondition'),
                        Child('OptionalBinding',