build.sh: Overwrite prerelease.txt if it exists, just like we do elsewhere

Author: cameel

scripts/build.sh

@@ -11,7 +11,7 @@ else
 fi
 
 if [[ $(git tag --points-at HEAD 2> /dev/null) == v* ]]; then
-    touch "${ROOTDIR}/prerelease.txt"
+    echo -n > prerelease.txt
 fi
 
 mkdir -p "$BUILDDIR"