The ornamental design for an iron, as shown and described.
1. Iron
Figure 1.1 is a perspective view; figure 1.2 is a left side view; figure 1.3 is a right side view; figure 1.4 is a front view; figure 1.5 is a back view; figure 1.6 is a top view and figure 1.7 is a bottom view.
The broken lines in the drawings illustrate boundaries that form no part of the claimed design.