Mobile Theme: Fix translation call.

Translation function should use context function.
See #9
Props @jeherve, @deckerweb

modules/minileven/theme/pub/minileven/image.php

@@ -84,7 +84,7 @@
 				</article><!-- #post-<?php the_ID(); ?> -->
 
 				<nav id="nav-single">
-					<h3 class="assistive-text"><?php _e( 'Image navigation', 'next-saturday' , 'jetpack' ); ?></h3>
+					<h3 class="assistive-text"><?php _ex( 'Image navigation', 'next-saturday' , 'jetpack' ); ?></h3>
 					<span class="nav-previous"><?php previous_image_link( false, __( '&laquo; Previous' , 'jetpack' ) ); ?></span>
 					<span class="nav-next"><?php next_image_link( false, __( 'Next &raquo; ' , 'jetpack' ) ); ?></span>
 				</nav><!-- #nav-single -->
@@ -95,4 +95,4 @@
 
 			</div><!-- #content -->
 		</div><!-- #primary -->
-<?php get_footer(); ?>
+<?php get_footer(); ?>