Bug report

Bug summary

When I use the command plt.savefig in order to create a pgf file (to include it in a LaTeX document), the symbol for the negative numbers writtent in the file is − (U+2212), while LaTeX waits this symbol - (U+002D)

Code for reproduction
fig.savefig("file.pgf", bbox_inches='tight')

Matplotlib version

• Operating system : Windows 10
• Matplotlib version : 3.0.0
• Matplotlib backend (print(matplotlib.get_backend())) : TkAgg
• Python version : 3.7.0