It's called an "Integration Manager" (singular)

Fixes https://github.com/vector-im/riot-web/issues/11256

This was finally annoying me enough to fix it.

res/css/views/settings/_IntegrationManager.scss

@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-.mx_IntegrationsManager .mx_Dialog {
+.mx_IntegrationManager .mx_Dialog {
     width: 60%;
     height: 70%;
     overflow: hidden;
@@ -23,22 +23,22 @@ limitations under the License.
     max-height: initial;
 }
 
-.mx_IntegrationsManager iframe {
+.mx_IntegrationManager iframe {
     background-color: #fff;
     border: 0px;
     width: 100%;
     height: 100%;
 }
 
-.mx_IntegrationsManager_loading h3 {
+.mx_IntegrationManager_loading h3 {
     text-align: center;
 }
 
-.mx_IntegrationsManager_error {
+.mx_IntegrationManager_error {
     text-align: center;
     padding-top: 20px;
 }
 
-.mx_IntegrationsManager_error h3 {
+.mx_IntegrationManager_error h3 {
     color: $warning-color;
 }