Travis - the source directory is _srcdist, not _srcdir

Reviewed-by: Stephen Henson <steve@openssl.org>
diff --git a/.travis.yml b/.travis.yml
index 0865817..3322543 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -64,7 +64,7 @@
           srcdir=.;
           cd _srcdist;
       else
-          srcdir=../_srcdir;
+          srcdir=../_srcdist;
           mkdir _build;
           cd _build;
           if which ccache >/dev/null; then