[FieldArray] extend React.Component (#42)

* [FieldArray] extend React.Component

* [FieldArray.test.js] fix unit test

* [FieldArray.test.js] fix unit test

* [FieldArray] fix unit test

* [FieldArray] fix unit test

Author: petermikitsh

src/FieldArray.js

@@ -31,7 +31,7 @@ type State = {
   state: ?FieldState
 }
 
-class FieldArray extends React.PureComponent<Props, State> {
+class FieldArray extends React.Component<Props, State> {
   context: ReactContext
   props: Props
   state: State

src/FieldArray.test.js

@@ -246,9 +246,9 @@ describe('FieldArray', () => {
     renderArray.mock.calls[0][0].fields.push('c')
     await sleep(2)
 
-    expect(renderArray).toHaveBeenCalledTimes(2)
-    expect(renderArray.mock.calls[1][0].meta.valid).toBe(false)
-    expect(renderArray.mock.calls[1][0].meta.error).toBe('Too long')
+    expect(renderArray).toHaveBeenCalledTimes(3)
+    expect(renderArray.mock.calls[2][0].meta.valid).toBe(false)
+    expect(renderArray.mock.calls[2][0].meta.error).toBe('Too long')
   })
 
   it('should provide forEach', () => {