fixed typo (facebook#20351)

Author: togami2864

packages/react-reconciler/src/ReactFiberWorkLoop.new.js

@@ -3260,7 +3260,7 @@ export function warnIfNotScopedWithMatchingAct(fiber: Fiber): void {
             '// for react-test-renderer:\n' +
             // Break up imports to avoid accidentally parsing them as dependencies.
             'import TestRenderer fr' +
-            "om react-test-renderer';\n" +
+            "om 'react-test-renderer';\n" +
             'const {act} = TestRenderer;\n' +
             '// ...\n' +
             'act(() => ...);',

packages/react-reconciler/src/ReactFiberWorkLoop.old.js

@@ -3260,7 +3260,7 @@ export function warnIfNotScopedWithMatchingAct(fiber: Fiber): void {
             '// for react-test-renderer:\n' +
             // Break up imports to avoid accidentally parsing them as dependencies.
             'import TestRenderer fr' +
-            "om react-test-renderer';\n" +
+            "om 'react-test-renderer';\n" +
             'const {act} = TestRenderer;\n' +
             '// ...\n' +
             'act(() => ...);',