[diff.decl] Fix typo (#1494)

Author: jwilk

source/compatibility.tex

@@ -576,7 +576,7 @@
 \rationale
 When comparing types in different translation units, \Cpp relies
 on name equivalence when C relies on structural equivalence.
-Regarding parameter types: since the type defined in an parameter list
+Regarding parameter types: since the type defined in a parameter list
 would be in the scope of the function, the only legal calls in \Cpp
 would be from within the function itself.
 \effect