The ornamental design for a printer, as shown and described.
1. Printer
1.1 : Front
1.2 : Back
1.3 : Left
1.4 : Right
1.5 : Top
1.6 : Bottom
1.7 : Perspective
1.8 : Front view of a second state
1.9 : Back view of a second state
1.10 : Left view of a second state
1.11 : Right view of a second state
1.12 : Top view of a second state
1.13 : Bottom view of a second state
1.14 : Perspective view of a second state
1.15 : Perspective view of a third state
Figs. 1.8-1.14 represent a second configuration with the input tray in an open position; fig. 1.15 represents a third configuration with input tray and pen door in an open position.