Explicitly configure shell for Spigot build

On Ubuntu, the default shell is dash, which supports Bourne shell syntax. The
Spigot build tools rely on Bash syntax, specifically Bash function declarations:

Bourne shell:

    applyPatches() {
      # ...
    }

Bash:

    function applyPatches() {
      # ...
    }

This commit overrides the default user shell for the build.

Author: benwebber

tasks/install/spigot.yml

@@ -6,6 +6,8 @@
   args:
     creates: spigot-{{ minecraft_version_latest | default(minecraft_version) }}.jar
     chdir: "{{ minecraft_home }}/build"
+  environment:
+    SHELL: /bin/bash
   become: true
   become_user: "{{ minecraft_user }}"