Fix javadoc for Exp.getUses() and Stmt.getUses() (#184)

Author: jjppp

src/main/java/pascal/taie/ir/exp/Exp.java

@@ -38,7 +38,7 @@ public interface Exp extends Serializable {
     Type getType();
 
     /**
-     * @return a list of expressions which are used by (contained in) this Exp.
+     * @return a set of expressions which are used by (contained in) this Exp.
      */
     default Set<RValue> getUses() {
         return Set.of();

src/main/java/pascal/taie/ir/stmt/Stmt.java

@@ -58,7 +58,7 @@ public interface Stmt extends Indexable, Serializable {
     Optional<LValue> getDef();
 
     /**
-     * @return a list of right-value expressions used in this Stmt.
+     * @return a set of right-value expressions used in this Stmt.
      */
     Set<RValue> getUses();