Fix running flow on travis and update flow (#9128)

* Fix running flow on travis and update flow

- ensure bootstrap is run before running flow as we need some generated files for correctly doing typechecks
- ensure that we only ignore the build directory inside the babel folder as currently we ignore everything because travis checks out into ‘/home/travis/build/’

* Fix all flow errors

packages/babel-parser/src/tokenizer/state.js

@@ -140,7 +140,10 @@ export default class State {
   // The first yield or await expression inside parenthesized expressions
   // and arrow function parameters. It is used to disallow yield and await in
   // arrow function parameters.
-  yieldOrAwaitInPossibleArrowParameters: ?N.YieldExpression;
+  yieldOrAwaitInPossibleArrowParameters:
+    | N.YieldExpression
+    | N.AwaitExpression
+    | null;
 
   // Token store.
   tokens: Array<Token | N.Comment>;