This is may build. After run it I get:
sh: D:UserDropboxApplicationsSoftwareVersioningSublimeTextDataPackages/SublimeBuildSystem/Uncrustify.sh: No such file or directory
So, we may see, the inverted slashes \ are being interpreted as escape characters. It is needed double \\ or / as used on the ending path.
{
"working_dir": "$file_path",
// "selector": "source.AmxxPawn, source.AMXX",
"shell": true,
"cmd": ["bash", "--login", "-i", "-c", "sh $packages/SublimeBuildSystem/Uncrustify.sh", "$file"],
"target": "ansi_color_build",
"syntax": "Packages/ANSIescape/ANSI.tmLanguage"
}