NetworkPkg: Reword PXE download message
NetworkPkg: Reword PXE download message

Fix a minor grammatical error in the PXE boot message.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Samer El-Haj-Mahmoud <69075e1ba2600094d95dfeb0aa01056bdaba053c@hpe.com>
Reviewed-by: Fu Siyuan <eef549df2036636f79f66102b4e2dc444721df8f@intel.com>

MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2