RunCommand: Return metrics as a float

Apparently, DBIx::Class doesn't handle columns with type 'double
precision' properly.

src/lib/Hydra/Plugin/RunCommand.pm

@@ -97,7 +97,7 @@ sub buildFinished {
                 my $j = {
                     name => $metric->name,
                     unit => $metric->unit,
-                    value => $metric->value,
+                    value => 0 + $metric->value,
                 };
                 push @{$json->{metrics}}, $j;
             }