Typo reporting `--hdu=0' (or `-h0')

[rmorales]

Summary:
Typo reporting  `--hdu=0' (or `-h0')

gnuastro version:
0.11

test image set:
https://cloud.iaa.csic.es/public.php?service=files&t=9344cdb85c640c7dd74446d8c266591d

command:
aststatistics 019_00.fits

result :
To fix the problem please add `--hdu=0' (or `-h0') to your command when 
calling Gnuastro's programs. For library users, please give a value of 
"0" to the HDU argument.

question:
Two different types of quotation marks are used to surround a single 
message.

suggestion:
Use just one type of quotation marks, for example neutral quotation 
marks (https://en.wikipedia.org/wiki/Quotation_mark) :

'--hdu=0' (or '-h0')