CI: add a temporary workaround for broken git describe

git describe picks 1.7.5 as a closest tag on 1.8 branch.
Temporary remove 1.7.5 tag to fix 1.8.x packages.

.travis.yml

@@ -108,6 +108,7 @@ matrix:
         compiler: gcc
 
 script:
+  - git tag -d 1.7.5
   - make -f .travis.mk ${TARGET}
 
 before_deploy: