Alphabetically sort filenames returned by Dir.glob

Sheldon#build uses Ruby's Dir.glob to locate all files with "config_" in
their filename. The order in which files are located in a filesystem
will vary between environments (and possibly Ruby versions), leading to
different behaviour of Sheldon#build across different hosts. This commit
alphabetically sorts the filenames retrieved by Dir.glob, thus
eliminating variance.

lib/sheldon/builder.rb

@@ -2,7 +2,7 @@ class Builder
   require "fileutils"
 
   def build(abs_build_path)
-    entries = Dir.glob(abs_build_path + "/*")
+    entries = Dir.glob(abs_build_path + "/*").sort
     master_content = entries.inject("") do |buffer, entry|
       is_config?(entry) ? add_entry_to_buffer(entry, buffer) : buffer
     end