add pecl yaml library, fixed composer hash

[BasilSnowman]

#14

Add pecl yaml library.
Fixed composer installer hash.

[andypost]

I'm sure better to file MR to alpine repo as pointed in #14

[BasilSnowman]

why alpine repo? we create containers for php. for internal needs.

[andypost]

Because it's easy to manage and install instead of building locally, also having this package in ALpine will bring more eyes and testers

PS Your approach more like anavarre/drucker@2ce24be but it will take more time and makes image size bigger

[andriyun]

@BasilSnowman need update branch and resolve conflicts

[andypost]

Also there's core issue about compatibility, not solved yet

https://www.drupal.org/node/2792877