Fix two issues i had when using the new buildpack code:

mkdir: cannot create directory `/app//.profile.d': File exists
 !     Heroku push rejected, failed to compile Erlang app

cp: cannot stat `/tmp/buildpack_bmoaig71iviz/opt/otp.sh': No such file or directory
 !     Heroku push rejected, failed to compile Erlang app

bin/compile

@@ -59,7 +59,9 @@ if [ ${PIPESTATUS[0]} -ne 0 ]; then
   exit 1
 fi
 
-mkdir ${PROFILE}
-cp ${bpdir}/opt/otp.sh ${PROFILE}
+if [ -f ${bpdir}/opt/otp.sh ]; then
+  mkdir -p ${PROFILE}
+  cp ${bpdir}/opt/otp.sh ${PROFILE}
+fi
 
 echo "-----> Build succeeded"