fix rstudio/bookdown#126 and also close rstudio/bookdown#142: use an …

…alternative form of chapter_name (due to the bug vubiostat/r-yaml#6, we cannot use R expressions in YAML that contains multibyte characters)

_bookdown.yml

@@ -1,5 +1,5 @@
 book_filename: r-ninja
-chapter_name: !expr "function(i) paste0('第', i, '章')"
+chapter_name: ["第", "章"]
 repo: https://github.com/yihui/r-ninja/
 output_dir: _book
 clean: [packages.bib, r-ninja.bbl]