Fix travis build issues
Fix travis build issues

This commit
- Upgrades go versions. Build fails for prior versions as they
do not use go modules
- Disables go vet for the "tip" till the issues are fixed for latest go version

Signed-off-by: manish <a9d79eea65b0c2019f8af02c53bb35240dcbd527@gmail.com>

syndtr/goleveldb