fix typo

bug1240930-253/mozilla/1455504-62a1.patch

@@ -63,7 +63,7 @@ diff --git a/python/mozbuild/mozbuild/backend/recursivemake.py b/python/mozbuild
 -            if isinstance(lib, (HostLibrary, HostRustLibrary)):
 -                backend_file.write_once('HOST_LIBS += %s/%s\n' %
 -                                        (pretty_relpath(lib), lib.import_name))
-+            i isinstance(lib, (HostRustLibrary)):
++            if isinstance(lib, (HostRustLibrary)):
 +                backend_file.write_once('HOST_LIBS += %s\n' %
 +                                        pretty_relpath(lib, lib.import_name))
 +