tools/built-release.sh: fix archives we produce.

We were tarring up the build dir, not the destination dir!  We did this
for 0.6.3 and nobody noticed :(

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

tools/build-release.sh

@@ -9,7 +9,7 @@ if [ x"$1" = x"--inside-docker" ]; then
     ./configure
     make -j3
     make install DESTDIR=/"$VER"
-    tar cvfz /release/clightning-"$VER".tar.gz -- *
+    cd /"$VER" && tar cvfz /release/clightning-"$VER".tar.gz -- *
     exit 0
 fi