Update mkreleasehdr.sh

fix date +%s errata

src/mkreleasehdr.sh

@@ -3,7 +3,7 @@ GIT_SHA1=`(git show-ref --head --hash=8 2> /dev/null || echo 00000000) | head -n
 GIT_DIRTY=`git diff --no-ext-diff 2> /dev/null | wc -l`
 BUILD_ID=`uname -n`"-"`date +%s`
 if [ -n "$SOURCE_DATE_EPOCH" ]; then
-  BUILD_ID=$(date -u -d "@$SOURCE_DATE_EPOCH" +%s 2>/dev/null || date -u -r "$SOURCE_DATE_EPOCH" +%s 2>/dev/null || date -u %s)
+  BUILD_ID=$(date -u -d "@$SOURCE_DATE_EPOCH" +%s 2>/dev/null || date -u -r "$SOURCE_DATE_EPOCH" +%s 2>/dev/null || date -u +%s)
 fi
 test -f release.h || touch release.h
 (cat release.h | grep SHA1 | grep $GIT_SHA1) && \