Updated build.bat to also copy lua51.dll

Author: levno-710

build.bat

@@ -4,4 +4,5 @@ RMDIR /s /q build
 MKDIR build
 glue.exe ./srlua.exe prometheus-main.lua build/prometheus.exe
 robocopy ./src ./build/lua /E>nul
+copy ./lua51.dll ./build/lua51.dll
 ECHO Done!