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/plugins/estree.js

@@ -300,7 +300,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
 
       if (node) {
         node.type = "Property";
-        if (node.kind === "method") node.kind = "init";
+        if (((node: any): N.ClassMethod).kind === "method") node.kind = "init";
         node.shorthand = false;
       }