Fix warning from shellcheck

shellcheck warning:

    In /tesseract/src/training/tesstrain_utils.sh line 209:
        TIMESTAMP=`date +%Y-%m-%d`
                  ^-- SC2006: Use $(..) instead of legacy `..`.

Signed-off-by: Stefan Weil <[email protected]>

Author: stweil

src/training/tesstrain_utils.sh

@@ -198,7 +198,7 @@ parse_flags() {
     fi
 
     # Location where intermediate files will be created.
-    TIMESTAMP=`date +%Y-%m-%d`
+    TIMESTAMP=$(date +%Y-%m-%d)
     TMP_DIR=$(mktemp -d -t ${LANG_CODE}-${TIMESTAMP}.XXX)
     TRAINING_DIR=${TMP_DIR}
     # Location of log file for the whole run.