C++: fix typo in qhelp

cpp/ql/src/Critical/UseAfterFree.qhelp

@@ -8,7 +8,7 @@
 <p>
 This rule finds accesses through a pointer of a memory location that has already been freed (i.e. through a dangling pointer). 
 Such memory blocks have already been released to the dynamic memory manager, and modifying them can lead to anything 
-from a segfault to memory corruption that would cause subsequent calls to the dynamic memory manger to behave 
+from a segfault to memory corruption that would cause subsequent calls to the dynamic memory manager to behave 
 erratically, to a possible security vulnerability.
 </p>