Fix typos and things

**what is the change?:**
- `migrade` -> `migrate`
- `15.* prop-types package` -> `v15.* prop-types package`

**why make this change?:**
Correctness

**test plan:**
`yarn test` and visual inspection

src/isomorphic/React.js

@@ -112,7 +112,7 @@ if (__DEV__) {
  didWarnPropTypesDeprecated,
  'Accessing PropTypes via the main React package is deprecated,' +
  ' and will be removed in React v16.0.' +
- ' Use the latest available 15.* prop-types package from npm instead.' +
+ ' Use the latest available v15.* prop-types package from npm instead.' +
  ' For info on usage, compatibility, migration and more, see ' +
  'https://fb.me/prop-types-docs',
  );
@@ -128,7 +128,7 @@ if (__DEV__) {
  'Accessing createClass via the main React package is deprecated,' +
  ' and will be removed in React v16.0.' +
  " Use a plain JavaScript class instead. If you're not yet " +
- 'ready to migrade, create-react-class v15.* is available ' +
+ 'ready to migrate, create-react-class v15.* is available ' +
  'on npm as a temporary, drop-in replacement. ' +
  'For more info see https://fb.me/react-create-class',
  );

src/isomorphic/__tests__/React-test.js

@@ -47,9 +47,9 @@ describe('React', () => {
  expect(console.warn.calls.argsFor(0)[0]).toContain(
  'Warning: Accessing createClass via the main React package is ' +
  'deprecated, and will be removed in React v16.0. ' +
- 'Use a plain JavaScript class instead. ' +
- "If you're not yet ready to migrade, create-react-class " +
- 'v15.* is available on npm as a temporary, drop-in replacement. ' +
+ "Use a plain JavaScript class instead. If you're not yet ready " +
+ 'to migrate, create-react-class v15.* is available on npm as ' +
+ 'a temporary, drop-in replacement. ' +
  'For more info see https://fb.me/react-create-class',
  );
  });
@@ -63,9 +63,9 @@ describe('React', () => {
  expect(console.warn.calls.argsFor(0)[0]).toContain(
  'Warning: Accessing PropTypes via the main React package is ' +
  'deprecated, and will be removed in React v16.0. ' +
- 'Use the latest available 15.* prop-types package from npm instead. ' +
- 'For info on usage, compatibility, migration and more, ' +
- 'see https://fb.me/prop-types-docs',
+ 'Use the latest available v15.* prop-types package from ' +
+ 'npm instead. For info on usage, compatibility, migration ' +
+ 'and more, see https://fb.me/prop-types-docs',
  );
  });
 });