software/theia: better inter-part dependencies

if yarn.lock is changed, part should be re-installed. This is only
useful during development.

software/theia/software.cfg

@@ -69,6 +69,7 @@ command = ${bash:location}/bin/bash -c "
   ${yarn:location}/bin/yarn theia build"
 location = ${buildout:parts-directory}/${:_buildout_section_name_}
 stop-on-error = true
+uses = ${yarn.lock:recipe}
 
 [yarn.lock]
 recipe = slapos.recipe.template