Add support for Alpine Abuild (APKBUILD) (#2934)

APKBUILD is a file containing "recipes" on how something should be
built/compiled. It's used by APK, the Alpine Linux package manager.

lib/linguist/languages.yml

@@ -147,6 +147,17 @@ Alloy:
   - .als
   ace_mode: text
 
+Alpine Abuild:
+  type: programming
+  group: Shell
+  aliases:
+  - abuild
+  - apkbuild
+  filenames:
+  - APKBUILD
+  tm_scope: source.shell
+  ace_mode: sh
+
 Ant Build System:
   type: data
   tm_scope: text.xml.ant