fix displayname searchbox to small on composeview

stylesheets/_session_theme_dark_left_pane.scss

@@ -190,6 +190,10 @@ $session-compose-margin: 20px;
   }
 }
 
+.user-search-dropdown {
+  width: 100%;
+}
+
 .session-search-input {
   height: 34px;
   width: 100%;

ts/components/session/UserSearchDropdown.tsx

@@ -66,7 +66,7 @@ export class UserSearchDropdown extends React.Component<Props, State> {
     const { selectedContact } = this.state;
 
     return (
-      <div>
+      <div className="user-search-dropdown">
         <SessionSearchInput
           searchString={this.props.searchTerm}
           onChange={this.updateSearchBound}