fix convert_txt command (#195)

Author: memsharded

extensions/commands/migrate/cmd_convert_txt.py

@@ -3,7 +3,13 @@
 from jinja2 import Template
 from conan.cli.command import conan_command
 from conan.api.output import cli_out_write
-from conans.client.loader_txt import ConanFileTextLoader
+
+# FIXME: This shouldn't be done, this is an internal Conan API and shouldn't be used
+# It is forbidden, and it can break anytime
+try:
+    from conan.internal.loader import ConanFileTextLoader
+except:
+    from conans.client.loader_txt import ConanFileTextLoader
 
 
 @conan_command(group="Extension", formatters={"text": cli_out_write})