.travis.yml: Add lzop

We need lzop now in order to make some FIT images that use LZO
compression on the contents.

Signed-off-by: Tom Rini <trini@konsulko.com>

.travis.yml

@@ -27,6 +27,7 @@ addons:
     - rpm2cpio
     - wget
     - device-tree-compiler
+    - lzop
 
 install:
  # Clone uboot-test-hooks