[fix] make books/user.pdf

Error:

  Configuration error:
  There is a programmable error in your configuration file:
  ...
  NameError: name 'DOCS_URL' is not defined
  make: *** [utils/makefile.sphinx:156: books/user.latex] Fehler 2

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

docs/user/conf.py

@@ -4,7 +4,7 @@
 project   = 'Searx User-HB'
 version   = release = VERSION_STRING
 
-intersphinx_mapping['searx'] = (DOCS_URL, None)
+intersphinx_mapping['searx'] = (brand.DOCS_URL, None)
 
 # Grouping the document tree into LaTeX files. List of tuples
 # (source start file, target name, title,