docs: revert textual changes in spec and make consistent

cx/policy/specs/policy.definitions.md

@@ -42,7 +42,7 @@ be used.
 ### 1.3 A Note on Json-Ld Prefixes
 
 Json-Ld prefixes are not show in the examples since the Json-Ld context includes term aliases that make prefixes
-optional for known constraint types. For example, assuming the `tx` prefix, `Membership` and `tx-policy:Membership` are equal
+optional for known constraint types. For example, assuming the `cx` prefix, `Membership` and `cx-policy:Membership` are equal
 and will be processed in the same way.
 
 # 2. Membership Constraint