Fix registering npm linked components

src/register-components.js

 const logger = require('@pubsweet/logger')
 const config = require('config')
+const requireRelative = require('require-relative')
 
 module.exports = app => {
   if (config.has('pubsweet.components')) {
     config.get('pubsweet.components').forEach(name => {
-      const component = require(name)
+      const component = requireRelative(name)
       logger.info('Registered component', name)
       const backendComponent = component.server || component.backend
       if (backendComponent) {