Replace very cute (ab)use of array to get first element with explicit awk

That is to overcome warnings from shellcheck

	In .clusterfuzzlite/build.sh line 8:
		hash=($(sha256sum "$file"))
			  ^------------------^ SC2207 (warning): Prefer mapfile or read -a to split command output (or quote to avoid splitting).

	In .clusterfuzzlite/build.sh line 9:
		cp "$file" "/tmp/oxigraph_$1/$hash"
									 ^---^ SC2128 (warning): Expanding an array without an index only gives the first element.

although original code is making a cute use of an array, if we are to follow
shellcheck and use mapfile or read -a - and then use explicit index -- makes it
just too cumbersome. IMHO  explicit awk would be easier to read etc.

.clusterfuzzlite/build.sh

@@ -5,7 +5,7 @@ function build_seed_corpus() {
   mkdir "/tmp/oxigraph_$1"
   for file in **/*."$2"
   do
-    hash=($(sha256sum "$file"))
+    hash=$(sha256sum "$file" | awk '{print $1;}')
     cp "$file" "/tmp/oxigraph_$1/$hash"
   done
   zip "$1_seed_corpus.zip" /tmp/"oxigraph_$1"/*