Add return type on "__toString" methods

src/Markup.php

@@ -27,7 +27,7 @@ class Markup implements \Countable, \JsonSerializable, \Stringable
         $this->charset = $charset;
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return $this->content;
     }

src/Token.php

@@ -40,7 +40,7 @@ final class Token
     ) {
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return \sprintf('%s(%s)', self::typeToString($this->type, true), $this->value);
     }

src/TokenStream.php

@@ -32,7 +32,7 @@ final class TokenStream
     ) {
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return implode("\n", $this->tokens);
     }