VBSP: Argument mismatch for -dumpstaticprops

[maxik34]

VBSP recognizes -dumpstaticprop while in the docs/VBSP help text it is -dumpstaticprops (plural).
Fix: In vbsp.cpp on line 1070 add letter "s" at the end of "-dumpstaticprop" string.

[ianherzing]

Submitted #1932 for this — one-character change aligning the argv matcher with the documented spelling from the help text. Happy to add a local-build screenshot if useful.