Fix broken AppImage building
Fix broken AppImage building

LinuxDeploy, the tool we use to build AppImage source was updated and
now creates the AppImage file with a name that is different than what
came before. This commit updates our single command that depends on that
filename to deal with the variability.

Previously files were named Pony_Compiler-x86_64.AppImage
Now they are Pony_Compiler-SOME_VERSION-x86_64.AppImage

cquinn/ponyc,cquinn/ponyc,kulibali/ponyc,dipinhora/ponyc,kulibali/ponyc,cquinn/ponyc,sgebbie/ponyc,sgebbie/ponyc,jemc/ponyc,sgebbie/ponyc,kulibali/ponyc,sgebbie/ponyc,jemc/ponyc,ponylang/ponyc,cquinn/ponyc,dipinhora/ponyc,sgebbie/ponyc,ponylang/ponyc,dipinhora/ponyc,kulibali/ponyc,jemc/ponyc,ponylang/ponyc