fix typos - syntax errors in config.js example

* in the example code for config.js in INSTALL.md
  contains three key-value-pairs not present in the example file
  'config.js.example' - these were appended without inserting a comma
  and the last two of these were commented out without removing
  the trailing comma - the example file 'config.js.example' is correct
  but using the INSTALL.md version causes the page render to halt prematurely
  making login impossible