Add missing python-sql dependency

INSTALL

@@ -6,6 +6,7 @@ Prerequisites
 
  * Python 3.4 or later (http://www.python.org/)
  * trytond (http://www.tryton.org/)
+ * python-sql (https://pypi.org/project/python-sql/)
 
 Installation
 ------------

setup.py

@@ -45,7 +45,7 @@ if minor_version % 2:
         'hg+http://hg.tryton.org/modules/%s#egg=%s-%s' % (
             name[8:], name, version))
 
-requires = []
+requires = ['python-sql']
 for dep in info.get('depends', []):
     if not re.match(r'(ir|res)(\W|$)', dep):
         requires.append(get_require_version('trytond_%s' % dep))