The ornamental design for a computermouse, as shown and described.
1. Computer mouse
1.1: Perspective
1.2: Front
1.3: Back
1.4: Left
1.5: Right
1.6: Top
1.7: Bottom
1.8: Reference
Reproduction 1.8shows the state of use with a top cover in different size; the broken lines are for the purpose of illustrating environment only and form no part of the claimed design.