Update tox.ini

Author: ElePT

tox.ini

@@ -7,7 +7,7 @@ skip_missing_interpreters = true
 [testenv]
 # CI: skip-next-line
 usedevelop = true
-install_command = pip install -c{toxinidir}/constraints.txt -U {opts:} {packages:}
+install_command = pip install -U {opts:} {packages:}
 setenv =
   VIRTUAL_ENV={envdir}
   LANGUAGE=en_US