Fixed capitalization, tests

src/Key/JWTPlaintextKey.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace NoccyLabs\SimpleJWT\Key;
+
+class JWTPlaintextKey implements KeyInterface
+{
+    private $key;
+
+    public function __construct(string $key)
+    {
+        $this->key = $key;
+    }
+
+    public function getBinaryKey(): string
+    {
+        return $this->key;
+    }
+}
+