Doc: Fix build error in Lua plugin documentation.
Doc: Fix build error in Lua plugin documentation.

dyrock/trafficserver,chitianhao/trafficserver,pbchou/trafficserver,pbchou/trafficserver,vmamidi/trafficserver,duke8253/trafficserver,chitianhao/trafficserver,dyrock/trafficserver,SolidWallOfCode/trafficserver,davidbz/trafficserver,dyrock/trafficserver,vmamidi/trafficserver,chitianhao/trafficserver,dyrock/trafficserver,duke8253/trafficserver,dyrock/trafficserver,duke8253/trafficserver,davidbz/trafficserver,vmamidi/trafficserver,chitianhao/trafficserver,dyrock/trafficserver,SolidWallOfCode/trafficserver,duke8253/trafficserver,bryancall/trafficserver,SolidWallOfCode/trafficserver,davidbz/trafficserver,duke8253/trafficserver,SolidWallOfCode/trafficserver,vmamidi/trafficserver,SolidWallOfCode/trafficserver,SolidWallOfCode/trafficserver,bryancall/trafficserver,dyrock/trafficserver,pbchou/trafficserver,chitianhao/trafficserver,davidbz/trafficserver,bryancall/trafficserver,pbchou/trafficserver,SolidWallOfCode/trafficserver,davidbz/trafficserver,pbchou/trafficserver,bryancall/trafficserver,bryancall/trafficserver,pbchou/trafficserver,davidbz/trafficserver,duke8253/trafficserver,chitianhao/trafficserver,vmamidi/trafficserver,duke8253/trafficserver,bryancall/trafficserver,chitianhao/trafficserver,vmamidi/trafficserver