Update firstapp.md
Update firstapp.md

简单修饰
Update firstapp.md
Update firstapp.md
Update firstapp.md

整章翻好
Merge pull request #14 from meteormatt/master

更新
Merge pull request #15 from meteormatt/master

MDN
Update devtools.md
Update devtools.md
Update firstapp.md
Update firstapp.md

change 【##总结】 --> 【## 总结】
Update devtools.md
Merge pull request #8 from lucyking/master

firstapp和devtools两章
Merge pull request #6 from MozillaChina/master

上游合并