Export dismissRuntimeErrors function (facebook#3414)

Author: ovidiuch

packages/react-error-overlay/src/index.js

@@ -87,7 +87,7 @@ function handleRuntimeError(errorRecord) {
   update();
 }
 
-function dismissRuntimeErrors() {
+export function dismissRuntimeErrors() {
   currentRuntimeErrorRecords = [];
   update();
 }