Update vtx-firmware-update.md

Author: czhou1972

docs/vtx-firmware-update.md

@@ -9,7 +9,7 @@ For Windows system:
 
 
 For Mac system:
-Great thanks to Gunther Votteler for developing the Mac utility to for the HDZero Programmer. Follow the directions here:
+Great thanks to Gunther Votteler for developing the Mac utility for the HDZero Programmer. Follow the directions here:
 https://github.com/gvotteler/hdzero-programmer-tool-mac