tox.ini: Fix toml extra specification for coverage target.

Signed-off-by: Chris PeBenito <pebenito@ieee.org>

Author: pebenito

tox.ini

@@ -15,8 +15,7 @@ commands        = pycodestyle setools/ setoolsgui/ tests/ seinfo seinfoflow sedt
 #setenv          = SETOOLS_COVERAGE = 1
 passenv         = {[testenv]passenv}
 deps            = {[testenv]deps}
-                  coverage>=6.0
-extras          = toml
+                  coverage[toml]>=6.0
 commands_pre    = coverage --version
                   coverage erase
                   {[testenv]commands_pre}