Make emoji picker search placeholder localizable

src/components/views/emojipicker/Search.tsx

@@ -63,7 +63,7 @@ class Search extends React.PureComponent<IProps> {
                 <input
                     autoFocus
                     type="text"
-                    placeholder="Search"
+                    placeholder={_t("Search")}
                     value={this.props.query}
                     onChange={ev => this.props.onChange(ev.target.value)}
                     onKeyDown={this.onKeyDown}