bugfix: request headers contains "_" should be case-insensitive matched.

[vm-001]

I hereby granted the copyright of the changes in this pull request to the authors of this lua-resty-core project.

Fix a bug that request header contains "_" unable to be case-insensitive matched. e.g.

-- Request with headers:
-- X_Foo_Header: foo

local value = ngx.req.get_headers()["X_Foo_Header"]  -- nil

[zhuizhuhaomeng]

@vm-001 you have removed spaces that should not be removed

[vm-001]

@zhuizhuhaomeng Ops, Looks like the IntelliJ IDEA is not intelligent at this moment. Fixed.

[vm-001]

@zhuizhuhaomeng I think the CI failure is not caused by the PR because I also found a similar failure in another empty PR(https://app.travis-ci.com/github/openresty/lua-resty-core/builds/260795767)

[vm-001]

Hi @zhuizhuhaomeng , May I know can this PR be merged?

[zhuizhuhaomeng]

@vm-001 The CI ran failed. Please rebase to the latest master branch code.

[zhuizhuhaomeng]

https://app.travis-ci.com/github/openresty/lua-resty-core/builds/261234448#L575 The CI failed. Please have a look at this one.

[vm-001]

https://app.travis-ci.com/github/openresty/lua-resty-core/builds/261234448#L575 The CI failed. Please have a look at this one.

Thanks for the reminder. I've fixed the test fails. But I saw the CI still fails, have no idea what's wrong.

[zhuizhuhaomeng]

This is still needed.

value = rawget(tb, (str_replace_char(key, '_', '-')))

[vm-001]

@zhuizhuhaomeng Yeah. I found the suggestion applied on the wrong line. I've made another suggestion to correct that.

[zhuizhuhaomeng]

add the following code to the top of the file

local str_find = string.find