[exercise1] Update image and rename variable.

exercises/exercise-basic/injection2pniproblem.hh

@@ -46,7 +46,7 @@ namespace Dumux {
  * apply on the left boundary.
  *
  * Gas is injected at the right boundary from 7 m to 15 m at a rate of
- * 0.001 kg/(s m), the remaining Neumann boundaries are no-flow
+ * 0.0001 kg/(s m), the remaining Neumann boundaries are no-flow
  * boundaries.
  *
  * At the Dirichlet boundaries a hydrostatic pressure and a gas saturation of zero a