Update yum references to dnf

All the cool kids use dnf already ;)

Change-Id: I36a56e4ffd230b7c93e792ca8fd8c7d138c43df7

Author: Jakub Ruzicka

rdopkg/actions/util/actions.py

@@ -36,7 +36,7 @@ def autocomplete():
         print(
             "You're missing the argcomplete python module. "
             "Install it using\n\n"
-            "    # yum install -y python-argcomplete\n\n"
+            "    # dnf install -y python-argcomplete\n\n"
             "or\n\n"
             "    # pip install argcomplete\n\n"
             "and run `rdopkg autocomplete` again.")

rdopkg/exception.py

@@ -58,7 +58,7 @@ class ModuleNotAvailable(RdopkgException):
 
 class RpmModuleNotAvailable(ModuleNotAvailable):
     msg_fmt = ("Module rpm is not available. It is required to parse .spec "
-               "files. Pro tip: `yum install rpm-python`")
+               "files. Pro tip: `dnf install rpm-python`")
 
 
 class InvalidAction(RdopkgException):