Bugfix: gen-version.sh: Replace bashism ("here string")

AUTHORS

@@ -56,3 +56,4 @@ capa66 <capa66@x204.com>
 Red_Wolf_2 <redwolf@wolfnexus.net>
 Mr O <notanatheist@gmail.com>
 James Hilliard <james.hilliard1@gmail.com>
+Dmitriy Korniychuk <dmitriy@korniychuk.org.ua>

gen-version.sh

@@ -14,7 +14,7 @@ if [ -z "$gitdesc" ]; then
 		gitdesc="$current"
 	fi
 fi
-version=$(sed 's/^bfgminer-//' <<<"$gitdesc")
+version=$(echo "$gitdesc" | sed 's/^bfgminer-//')
 cat <<EOF
 #define BFG_GIT_DESCRIBE "$gitdesc"
 #ifdef VERSION