Update dockerignore ignore dist and sites

As of now, it does nothing (`/dist/` doesn't filter the dist folder)
and sending anything from `dist` doesn't make sense as it's mounted
anyway.

Removing the traefik binary from whitelist as the integration script
compiles the binary before running, so we don't need to send it via
the build context.

Signed-off-by: Vincent Demeester <vincent@sbr.pm>

.dockerignore

@@ -1,3 +1,2 @@
-/dist/
+dist/
-!/dist/traefik
+site/
-/site/