Added more info to the plug-ins load fail.

Trying to see why it fails (not in my docker image?!)

kibot/kiplot.py

@@ -59,9 +59,9 @@ def _import(name, path):
     mod = module_from_spec(spec)
     try:
         spec.loader.exec_module(mod)
-    except ImportError:
+    except ImportError as e:
         trace_dump()
-        logger.error('Unable to import plug-ins')
+        logger.error('Unable to import plug-ins: '+str(e))
         exit(WRONG_INSTALL)