BUGFIX use the build_dir key rather than "_build"
BUGFIX use the build_dir key rather than "_build"

Now I'm happy with the fix, sinan can build standalone apps and the fix seems
clean enough.

For the record, the fix goes from 91fd2e4b48dd9073dbe1dfa2e5d7f997c1de220d to
this commit

Signed-off-by: Jordan Wilberding <c75c9afa7ab32355502e631bdcd27e5db15b49c6@gmail.com>

erlware-deprecated/sinan,ericbmerritt/sinan,erlware-deprecated/sinan,ericbmerritt/sinan,ericbmerritt/sinan,erlware-deprecated/sinan