Flip snap packaging's grade to stable
Flip snap packaging's grade to stable

This change allows downstream packagers to publish the snap to the
candidate and stable channels.

Signed-off-by: 林博仁(Buo-ren, Lin) <e1a755dad2798d70422023dceee1245c3d6b4517@gmail.com>

tesseract-ocr/tesseract,UB-Mannheim/tesseract,jbarlow83/tesseract,stweil/tesseract,UB-Mannheim/tesseract,stweil/tesseract,jbarlow83/tesseract,stweil/tesseract,tesseract-ocr/tesseract,UB-Mannheim/tesseract,jbarlow83/tesseract,UB-Mannheim/tesseract,stweil/tesseract,tesseract-ocr/tesseract,amitdo/tesseract,tesseract-ocr/tesseract,amitdo/tesseract,stweil/tesseract,amitdo/tesseract,jbarlow83/tesseract,amitdo/tesseract,UB-Mannheim/tesseract,amitdo/tesseract,tesseract-ocr/tesseract,jbarlow83/tesseract