use /tmp and not user's Downloads dir

pEpMacOSAdapter/pEpUpdater.mm

@@ -106,11 +106,7 @@ NSString* CONFIG_PATH = @"/Library/Application Support/pEp/Updater";
     NSLog(@"using key from %s", keyfile.c_str());
 
     NSString* cwd = [NSFileManager defaultManager].currentDirectoryPath;
-    NSURL* dirurl = [[[NSFileManager defaultManager]
-        URLsForDirectory:NSDownloadsDirectory inDomains:NSUserDomainMask]
-        lastObject];
-
-    NSString* dir = [dirurl path];
+    NSString* dir = @"/tmp";
 
     [[NSFileManager defaultManager] changeCurrentDirectoryPath:dir];
     std::string _filename;