Update img-allowed-roles.html (#470)

Author: scottaohara

tests/img-allowed-roles.html

@@ -83,6 +83,7 @@ <h3>Test 1</h3>
 					<p><img src=# alt=switch role=switch aria-checked=false tabindex="0"></p>
 					<p role=tablist><img src=# alt=tab tabindex=0 role=tab aria-selected=true></p>
 					<p role=tree><img src=# alt=treeitem role=treeitem tabindex=0></p>
+					<p><img src=# alt=doc-cover role=doc-cover></p>
 
 					<p>with title</p>
 					<p><img src=# title=image role=img></p>
@@ -101,6 +102,7 @@ <h3>Test 1</h3>
 					<p><img src=# title=switch role=switch aria-checked=false tabindex="0"></p>
 					<p role=tablist><img src=# title=tab tabindex=0 role=tab aria-selected=true></p>
 					<p role=tree><img src=# title=treeitem role=treeitem tabindex=0></p>
+					<p><img src=# title=doc-cover role=doc-cover></p>
 
 					<p>with aria-label</p>
 					<p><img src=# aria-label=image role=img></p>
@@ -119,6 +121,7 @@ <h3>Test 1</h3>
 					<p><img src=# aria-label=switch role=switch aria-checked=false tabindex="0"></p>
 					<p role=tablist><img src=# aria-label=tab tabindex=0 role=tab aria-selected=true></p>
 					<p role=tree><img src=# aria-label=treeitem role=treeitem tabindex=0></p>
+					<p><img src=# aria-label=doc-cover role=doc-cover></p>
 
 					<p id=al>with aria-labelledby</p>
 					<p><img src=# aria-labelledby=al role=img></p>
@@ -137,6 +140,7 @@ <h3>Test 1</h3>
 					<p><img src=# aria-labelledby=al role=switch aria-checked=false tabindex="0"></p>
 					<p role=tablist><img src=# aria-labelledby=al tabindex=0 role=tab aria-selected=true></p>
 					<p role=tree><img src=# aria-labelledby=al role=treeitem tabindex=0></p>
+					<p><img src=# aria-labelledby=al role=doc-cover></p>
 				</div>
 
 				<p><strong>Expected result:</strong>