term: fix longstanding bug with imagecat

Sometimes, I'd notice that imgcat would have a weird aspect.
I stumbled across the root cause while debugging something else:
the order of the pixel width and height was flipped here.

term/src/terminal.rs

@@ -75,8 +75,8 @@ impl Terminal {
             state: TerminalState::new(
                 physical_rows,
                 physical_cols,
-                pixel_height,
                 pixel_width,
+                pixel_height,
                 config,
                 term_program,
                 term_version,