puppet: Update package name for boto-on-python3.
puppet: Update package name for boto-on-python3.

The python3-boto3 package is the maintained fork that supports Python
3; it was renamed in Ubuntu Bionic from the original Ubuntu Xenial name.

shubhamdhama/zulip,showell/zulip,timabbott/zulip,brainwane/zulip,rht/zulip,kou/zulip,showell/zulip,rht/zulip,zulip/zulip,timabbott/zulip,kou/zulip,shubhamdhama/zulip,showell/zulip,kou/zulip,rht/zulip,kou/zulip,rht/zulip,hackerkid/zulip,kou/zulip,rht/zulip,showell/zulip,brainwane/zulip,showell/zulip,synicalsyntax/zulip,shubhamdhama/zulip,punchagan/zulip,synicalsyntax/zulip,zulip/zulip,hackerkid/zulip,timabbott/zulip,synicalsyntax/zulip,andersk/zulip,hackerkid/zulip,showell/zulip,timabbott/zulip,hackerkid/zulip,rht/zulip,eeshangarg/zulip,brainwane/zulip,showell/zulip,andersk/zulip,shubhamdhama/zulip,hackerkid/zulip,andersk/zulip,brainwane/zulip,synicalsyntax/zulip,shubhamdhama/zulip,timabbott/zulip,zulip/zulip,shubhamdhama/zulip,eeshangarg/zulip,hackerkid/zulip,timabbott/zulip,eeshangarg/zulip,punchagan/zulip,eeshangarg/zulip,punchagan/zulip,andersk/zulip,shubhamdhama/zulip,punchagan/zulip,zulip/zulip,zulip/zulip,eeshangarg/zulip,andersk/zulip,punchagan/zulip,punchagan/zulip,timabbott/zulip,brainwane/zulip,andersk/zulip,eeshangarg/zulip,punchagan/zulip,synicalsyntax/zulip,kou/zulip,andersk/zulip,eeshangarg/zulip,rht/zulip,synicalsyntax/zulip,hackerkid/zulip,brainwane/zulip,kou/zulip,zulip/zulip,zulip/zulip,brainwane/zulip,synicalsyntax/zulip