Fixed errors caused by "self" in interfaces

+ Fixed an error that was caused by the presence of "self" in type hinting inside interfaces

src/Api/Abstracts/AbstractApiRequester.php

@@ -131,7 +131,7 @@ abstract class AbstractApiRequester implements ApiRequesterInterface, RequestCha
      * @param Client $client
      * @return self
      */
-    public function setClient(Client &$client): self {
+    public function setClient(Client &$client) {
         $this->client = $client;
         return $this;
     }
@@ -154,7 +154,7 @@ abstract class AbstractApiRequester implements ApiRequesterInterface, RequestCha
      * @param string $authToken
      * @return self
      */
-    public function setAuthToken(string $authToken): self {
+    public function setAuthToken(string $authToken) {
         $this->authToken = $authToken;
         return $this;
     }

src/Api/Interfaces/ApiRequesterInterface.php

@@ -33,7 +33,7 @@ interface ApiRequesterInterface
      * @param Client $client
      * @return self
      */
-    public function setClient(Client &$client): self;
+    public function setClient(Client &$client);
 
     /**
      * Get the authentication token
@@ -52,7 +52,7 @@ interface ApiRequesterInterface
      * @param string $authToken
      * @return self
      */
-    public function setAuthToken(string $authToken): self;
+    public function setAuthToken(string $authToken);
 
     /**
      * @return $this

src/Model/Abstracts/AbstractApiModel.php

@@ -95,7 +95,7 @@ abstract class AbstractApiModel implements ApiModelInterface, JsonSerializable,
      * @param Client $client
      * @return self
      */
-    public function setClient(Client &$client): self {
+    public function setClient(Client &$client) {
         $this->client = $client;
         return $this;
     }

src/Model/Interfaces/ApiModelInterface.php

@@ -69,6 +69,6 @@ interface ApiModelInterface
      * @param Client $client
      * @return self
      */
-    public function setClient(Client &$client): self;
+    public function setClient(Client &$client);
 
 }