fix typo for glibcxx debug

9 jobs for v2.1rc1 in 6 minutes and 41 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #83431
VS2015
VS2015-32-bit

00:01:26

passed #83430
VS2015
VS2015-64-bit

00:01:31

passed #83429
VS2017
VS2017-32-bit

00:01:19

passed #83428
VS2015
VS2017-64-bit

00:01:29

passed #83425
Linux
clang-c++11

00:04:51

passed #83427
Linux
cppcheck

00:03:27

passed #83432
Linux
doc

00:00:09

passed #83424
Linux
gcc-c++11

00:04:34

passed #83426
Apple
macos-c++11

00:01:53