pop!_os synonym for ubuntu. Use deb package manager.

Summary:
Use Deb package manager on Pop! OS.

X-link: facebook/folly#2135

Reviewed By: Gownta

Differential Revision: D53441949

Pulled By: Orvid

fbshipit-source-id: a88f01aa5d251a57005a050c0fd7068f187a15a8

build/fbcode_builder/getdeps/platform.py

@@ -270,7 +270,7 @@ def get_package_manager(self):
             return "homebrew"
         if self.distro in ("fedora", "centos", "centos_stream"):
             return "rpm"
-        if self.distro.startswith(("debian", "ubuntu")):
+        if self.distro.startswith(("debian", "ubuntu", "pop!_os")):
             return "deb"
         return None