code: function putCache() {
        return new Promise(function(resolve, reject) {
          // make the cache key
          let key = getKey();
  
          // adapt the image
          adapt(function(err, stdout, stderr) {
            if (err) {
              return reject(err);
            }
  
            // convert the new image stream to buffer
            stream2buffer(stdout, function(err, buffer) {
              if (err) {
                return reject(err);
              }
  
              if (!buffer || !buffer.length) {
                return resolve(buffer);
              }
  
              // put the buffer in the cache
              put(key, buffer, function(err, data) {
                if (err) {
                  log(`Cache set failure: ${err instanceof Error ? err.message : err}`);
                }
  
                // return the buffer
                resolve(buffer);
              });
            });
          });
        });
      }
docs: Creates an adapted image buffer | puts it in the cache | returns the buffer
  
  @returns {Promise}