Update pack.js

[johnx7271]

rSourceMap is used to strip the sourcemap embeding in composite js files, so the g flag is not needed, and the extra newline should be added to the pattern, so to remove it with the entire line.

[2betop]

之前是担心 sourceMap 的行数对不上号，这事还得确认。

[johnx7271]

你可以测试一下。不过，我看没有问题。