[files_external] Fix phpdoc

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

apps/files_external/lib/Lib/Auth/AuthMechanism.php

@@ -80,7 +80,7 @@ class AuthMechanism implements \JsonSerializable {
 
 	/**
 	 * @param string $scheme
-	 * @return self
+	 * @return $this
 	 */
 	public function setScheme($scheme) {
 		$this->scheme = $scheme;

apps/files_external/lib/Lib/FrontendDefinitionTrait.php

@@ -49,7 +49,7 @@ trait FrontendDefinitionTrait {
 
 	/**
 	 * @param string $text
-	 * @return self
+	 * @return $this
 	 */
 	public function setText($text) {
 		$this->text = $text;

apps/files_external/lib/Lib/IdentifierTrait.php

@@ -46,7 +46,7 @@ trait IdentifierTrait {
 
 	/**
 	 * @param string $identifier
-	 * @return self
+	 * @return $this
 	 */
 	public function setIdentifier($identifier) {
 		$this->identifier = $identifier;