make join button relative url

Signed-off-by: Toshaan Bharvani <toshaan@vantosh.com>

themes/openpowerfoundation/layouts/partials/navbar.html

@@ -81,7 +81,7 @@
 							class="visually-hidden">Youtube</span></a>
 				</div>
 					<div class="header__contact-btn join-us-button desktop-view">
-						<a class="d-block btn-outline-primary btn-sm btn" href="/join">Join</a>
+						<a class="d-block btn-outline-primary btn-sm btn" href="{{ "/join/" | relURL }}">Join</a>
 					</div>
 					<div class="header__login-btn login-button desktop-view">
 						<a class="d-block btn-outline-primary btn-sm btn" href="https://portal.openpower.foundation/">Login</a>