修理 matplotlib 中文顯示錯誤

fix_matplotlib_chinese.md

1. 取得字體 (e.g. Droid-Sans-Fallback.ttf) 放到 <venv>/lib/python3.8/site-packages/matplotlib/mpl-data/fonts/ttf/

2. 編輯 <venv>/lib/python3.8/site-packages/matplotlib/mpl-data/matplotlibrc:257

   反註解兩行，把字體名稱加上去，注意到 Droid-Sans-Fallback 的 - 要用 代替，並且放在最前面

   - #font.family:  sans-serif
   + font.family:  sans-serif
   #font.style:   normal
   #font.variant: normal
   #font.weight:  normal
   #font.stretch: normal
   #font.size:    10.0
   
   #font.serif:      DejaVu Serif, Bitstream Vera Serif, Computer Modern Roman, New Century Schoolbook, Century Schoolbook L, Utopia, ITC Bookman, Bookman, Nimbus Roman No9 L, Times New Roman, Times, Palatino, Charter, serif
   - #font.sans-serif: DejaVu Sans, Bitstream Vera Sans, Computer Modern Sans Serif, Lucida Grande, Verdana, Geneva, Lucid, Arial, Helvetica, Avant Garde, sans-serif
   + font.sans-serif: Droid Sans Fallback, DejaVu Sans, Bitstream Vera Sans, Computer Modern Sans Serif, Lucida Grande, Verdana, Geneva, Lucid, Arial, Helvetica, Avant Garde, sans-serif
   #font.cursive:    Apple Chancery, Textile, Zapf Chancery, Sand, Script MT, Felipa, Comic Neue, Comic Sans MS, cursive
   #font.fantasy:    Chicago, Charcoal, Impact, Western, Humor Sans, xkcd, fantasy
   #font.monospace:  DejaVu Sans Mono, Bitstream Vera Sans Mono, Computer Modern Typewriter, Andale Mono, Nimbus Mono L, Courier New, Courier, Fixed, Terminal, monospace

3. 刪除 ~/.cache/matplotlib/