dont let placeholder show scrollbar when composer is narrow

Author: bwindels

res/css/views/rooms/_BasicMessageComposer.scss

@@ -42,7 +42,7 @@ limitations under the License.
  white-space: pre-wrap;
  word-wrap: break-word;
  outline: none;
- overflow-x: auto;
+ overflow-x: hidden;
 
  span.mx_UserPill, span.mx_RoomPill {
  padding-left: 21px;