Fix travis builds

Travis doesn't seem to know about 'expr'

Reviewed-by: Emilia Käsper <emilia@openssl.org>

.travis.yml

@@ -83,7 +83,7 @@ before_script:
     - cd ..
 
 script:
-    - if expr "$CONFIG_OPTS" : "--unified"; then
+    - if echo "$CONFIG_OPTS" | grep "--unified" >/dev/null; then
           cd _build;
       else
           cd _srcdist;