fix build issue on Alpinelinux

[zaoqi]

Additional Information
dependencies on Alpinelinux:

bash wget git build-base gnupg zip subversion automake libtool patch zlib-dev cairo-dev openssl-dev cmake autoconf automake fuse-dev vim desktop-file-utils gtest-dev libxft-dev librsvg-dev curl ncurses-dev texinfo gdb xz libffi-dev gettext-dev argp-standalone

[probonopd]

Getting

-- Checking for module 'librsvg-2.0'
--   No package 'librsvg-2.0' found
CMake Error at /usr/share/cmake-3.10/Modules/FindPkgConfig.cmake:415 (message):
  A required package was not found

Any idea why this is happening only in one of the builds @TheAssassin?

[TheAssassin]

Pretty obvious. You're not installing the dependencies. Come on, it's all in that message.

[probonopd]

@TheAssassin he is installing librsvg-dev though... and that seems to be version 2, at least in Alpine edge: https://pkgs.alpinelinux.org/package/edge/community/x86_64/librsvg-dev

[TheAssassin]

@probonopd I don't have time to debug this. Probably the 32-bit headers are missing, so librsvg-dev:i386 would need to be installed. The error is in the AppImageBuild build, though, so you can't install this dependency from here. In any case, I expect contributors to sort out build issues they introduce themselves.

[probonopd]

Edit: Hi @zaoqi we highly appreciate this pull request. In order for it to be merged it needs to pass the Travis CI build "green". The error may be on our side. Please give us some time.

亲爱的朋友，我们非常感谢。谢谢。为了合并它，它需要通过特拉维斯CI来构建。绿色，不是红色。再次感谢您的宝贵贡献。错误可能站在我们这边。请给我们一些时间。

[TheAssassin]

(just add changes to this PR until it builds green)

Err, no. Again, the build issue is likely because there is a dependency missing in our CentOS 6 Docker image we use to build most build tools. It's called AppImageBuild.

In general a bad advice, it's like, "I keep drinking diet coke but I don't lose weight"...

[zaoqi]

@probonopd The failure of CI is obviously not caused by this PR.
The build issue may be introduced by 4d6f5f3

[lockie]

Would love to actually have the ability to build AppImage in Apine Linux, how about merging this?

[probonopd]

@lockie first we need the build to become "green"...