Plugin list outputs nothing when no plugins are installed

[pskrbasu]

When no plugins are installed, plugin list should output an empty table.

v0.19.5

binaek@Turingmbp steampipe % steampipe plugin list --install-dir ~/test_install
+------------------+---------+-------------+
| Installed Plugin | Version | Connections |
+------------------+---------+-------------+
+------------------+---------+-------------+

v0.20.12

binaek@Turingmbp steampipe % steampipe plugin list --install-dir ~/test_install
binaek@Turingmbp steampipe %