hugolib: Improve error message for bad taxonomy weights
hugolib: Improve error message for bad taxonomy weights

Error is now "Unable to convert taxonomy weight []string{"40"} to int
for variables/files.md"

gohugoio/hugo,fedelibre/hugo,anthonyfok/hugo,mdhender/hugo,gohugoio/hugo,anthonyfok/hugo,mdhender/hugo,mdhender/hugo,mdhender/hugo,anthonyfok/hugo,fedelibre/hugo,fedelibre/hugo,gohugoio/hugo,fedelibre/hugo