restore accidentally omitted trailing period.

Author: haikusw

include/swift/AST/ASTNode.h

@@ -11,7 +11,7 @@
 //===----------------------------------------------------------------------===//
 //
 // This file defines the ASTNode, which is a union of Stmt, Expr, Decl,
-// Pattern, TypeRepr, StmtCondition, and CaseLabelItem
+// Pattern, TypeRepr, StmtCondition, and CaseLabelItem.
 //
 //===----------------------------------------------------------------------===//