Travis - the source directory is _srcdist, not _srcdir

Reviewed-by: NStephen Henson <steve@openssl.org>

.travis.yml

@@ -64,7 +64,7 @@ before_script:
           srcdir=.;
           cd _srcdist;
       else
-          srcdir=../_srcdir;
+          srcdir=../_srcdist;
           mkdir _build;
           cd _build;
           if which ccache >/dev/null; then