bugfix(buildUpdate): export BuildUpdate from watch rather than build

ionic-team#366 (comment)

Author: alan-agius4

src/index.ts

@@ -1,4 +1,4 @@
-export { build, buildUpdate } from './build';
+export { build } from './build';
 export { bundle, bundleUpdate } from './bundle';
 export { clean } from './clean';
 export { cleancss } from './cleancss';
@@ -9,7 +9,7 @@ export { ngc } from './ngc';
 export { sass, sassUpdate } from './sass';
 export { transpile } from './transpile';
 export { uglifyjs } from './uglifyjs';
-export { watch } from './watch';
+export { watch, buildUpdate } from './watch';
 export * from './util/config';
 export * from './util/helpers';
 export * from './util/interfaces';