Added missing slash while setting directories

Hi, many thanks for this buildpack!!

While using it, I noticed that a slash was missing setting the TESSERACT_OCR_DIR. Without it, the paths are wrong set and point to "/appvendor/..." instead of "/app/vendor/...".

-TESSERACT_OCR_DIR=${HOME}vendor/tesseract-ocr
+TESSERACT_OCR_DIR=${HOME}/vendor/tesseract-ocr 

cheers,
Alberto