ipc: s/floating-nodes/floating_nodes for consistency

testcases/t/16-nestedcons.t

@@ -26,7 +26,7 @@ my $expected = {
     focused => 0,
     urgent => 0,
     border => 0,
-    'floating-nodes' => ignore(),
+    'floating_nodes' => ignore(),
 };
 
 cmp_deeply($tree, $expected, 'root node OK');

testcases/t/22-split.t

@@ -76,7 +76,7 @@ sub sum_nodes {
     return 0 if !@{$nodes};
 
     my @children = (map { @{$_->{nodes}} } @{$nodes},
-                    map { @{$_->{'floating-nodes'}} } @{$nodes});
+                    map { @{$_->{'floating_nodes'}} } @{$nodes});
 
     return @{$nodes} + sum_nodes(\@children);
 }

testcases/t/lib/i3test.pm

@@ -112,7 +112,7 @@ sub get_focused {
         $lf = $focused[0];
         last unless defined($con->{focus});
         @focused = @{$con->{focus}};
-        @cons = grep { $_->{id} == $lf } (@{$con->{nodes}}, @{$con->{'floating-nodes'}});
+        @cons = grep { $_->{id} == $lf } (@{$con->{nodes}}, @{$con->{'floating_nodes'}});
         $con = $cons[0];
     }