Python 3's: avoid %-formatting, f-strings as a new way

[mozga-intel]

Python 3's f-Strings: An Improved String Formatting Syntax; Issue comes from: #658

CI jobs fail because %-formatting is obsolete: an error message:

+ make lint
scripts/lint.py dmlc "all" include src scripts --exclude_path include/dmlc/concurrentqueue.h include/dmlc/blockingconcurrentqueue.h
************* Module lint
 scripts/lint.py:42: convention (C0209, consider-using-f-string, LintHelper._print_summary_map) Formatting a regular string which could be a f-string
 scripts/lint.py:46: convention (C0209, consider-using-f-string, LintHelper._print_summary_map) Formatting a regular string which could be a f-string
 scripts/lint.py:114: convention (C0209, consider-using-f-string, LintHelper.print_summary) Formatting a regular string which could be a f-string