Use most current manifest_data

[sanderhahn]

Sapper build seemed one step behind changes, this PR intends to fix it.

Example of trouble experienced:

$ touch src/routes/xyz.svelte
$ ls __sapper__/dev/client/xyz*
ls: __sapper__/dev/client/xyz*: No such file or directory

$ touch src/routes/xyz2.svelte
$ ls __sapper__/dev/client/xyz*
__sapper__/dev/client/xyz.a25908c7.js

$ touch src/routes/xyz3.svelte
$ ls __sapper__/dev/client/xyz*
__sapper__/dev/client/xyz.a25908c7.js
__sapper__/dev/client/xyz2.02d1ee4f.js

[Conduitry]

Does this also fix stuff like #611?

[sanderhahn]

This PR does fix the following, which hopefully would be similar to issue #611:

$ echo 'export function get(req, res) { res.end("Hello\n"); }' >src/routes/hello.txt.js
$ curl -i "http://localhost:3000/hello.txt"
HTTP/1.1 404 Not Found

$ touch src/routes/x.svelte
$ curl -i 'http://localhost:3000/hello.txt'
HTTP/1.1 200 OK

[Conduitry]

Released in 0.27.5.