style(MatrixTestResult): Increase column width for duration

[pmhahn]

4em is too narrow for texts like 6 hr 17 min to fit into: It is shown on two lines as:

6 hr 17
min

The German translation is even worse, which spans 4 lines:

6
Stunden
17
Minuten

which make the table take up too much space.

Testing done

# jar xf matrix-project.jar hudson/tasks/test/MatrixTestResult/index.jelly
# vi  hudson/tasks/test/MatrixTestResult/index.jelly
# jar uf matrix-project.jar hudson/tasks/test/MatrixTestResult/index.jelly
# restart jenkins

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