Replace <--> by <>
Replace <--> by <>

According to the discussion at PR #1085.

opencog/link-grammar,ampli/link-grammar,linas/link-grammar,ampli/link-grammar,ampli/link-grammar,ampli/link-grammar,linas/link-grammar,linas/link-grammar,ampli/link-grammar,linas/link-grammar,opencog/link-grammar,linas/link-grammar,opencog/link-grammar,linas/link-grammar,opencog/link-grammar,ampli/link-grammar,opencog/link-grammar,opencog/link-grammar,linas/link-grammar,ampli/link-grammar,ampli/link-grammar,ampli/link-grammar,opencog/link-grammar,linas/link-grammar,linas/link-grammar,opencog/link-grammar,opencog/link-grammar