[AIRFLOW-XXX] Correct typos in UPDATING.md (#4242)
[AIRFLOW-XXX] Correct typos in UPDATING.md (#4242)

Started with "habe", "serever" and "certificiate" needing to be:
  "have", "server", and "certificate".
Ran a check, ignoring British and US accepted spellings.
Kept jargon. EG admin, aync, auth, backend, config, dag, s3, utils, etc.
Took exception to: "num of dag run" meaning "number of dag runs",
  "upness" is normally for quarks,
  "url" being lower-case, and
  sftp example having an excess file ending.
Python documentation writes "builtin" hyphenated, cases "PYTHONPATH".
Gave up on mixed use of "dag" and "DAG" as well as long line lengths.
malmiron/incubator-airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,airbnb/airflow,cfei18/incubator-airflow,nathanielvarona/airflow,nathanielvarona/airflow,wileeam/airflow,Fokko/incubator-airflow,Fokko/incubator-airflow,fenglu-g/incubator-airflow,Fokko/incubator-airflow,malmiron/incubator-airflow,sekikn/incubator-airflow,airbnb/airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,nathanielvarona/airflow,airbnb/airflow,sekikn/incubator-airflow,spektom/incubator-airflow,sekikn/incubator-airflow,dhuang/incubator-airflow,malmiron/incubator-airflow,mtagle/airflow,DinoCow/airflow,spektom/incubator-airflow,apache/incubator-airflow,mrkm4ntr/incubator-airflow,wooga/airflow,malmiron/incubator-airflow,apache/airflow,DinoCow/airflow,wileeam/airflow,mtagle/airflow,bolkedebruin/airflow,Fokko/incubator-airflow,apache/airflow,cfei18/incubator-airflow,dhuang/incubator-airflow,mistercrunch/airflow,apache/incubator-airflow,adamhaney/airflow,r39132/airflow,lyft/incubator-airflow,jgao54/airflow,DinoCow/airflow,wileeam/airflow,adamhaney/airflow,cfei18/incubator-airflow,sekikn/incubator-airflow,adamhaney/airflow,spektom/incubator-airflow,danielvdende/incubator-airflow,mistercrunch/airflow,r39132/airflow,cfei18/incubator-airflow,fenglu-g/incubator-airflow,mistercrunch/airflow,Acehaidrey/incubator-airflow,wooga/airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,artwr/airflow,mrkm4ntr/incubator-airflow,jgao54/airflow,jgao54/airflow,apache/airflow,DinoCow/airflow,danielvdende/incubator-airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,lyft/incubator-airflow,nathanielvarona/airflow,wooga/airflow,spektom/incubator-airflow,wooga/airflow,mistercrunch/airflow,artwr/airflow,airbnb/airflow,danielvdende/incubator-airflow,artwr/airflow,apache/incubator-airflow,nathanielvarona/airflow,bolkedebruin/airflow,apache/airflow,mtagle/airflow,dhuang/incubator-airflow,wileeam/airflow,mrkm4ntr/incubator-airflow,adamhaney/airflow,apache/incubator-airflow,r39132/airflow,apache/airflow,fenglu-g/incubator-airflow,fenglu-g/incubator-airflow,danielvdende/incubator-airflow,dhuang/incubator-airflow,r39132/airflow,artwr/airflow,cfei18/incubator-airflow,mrkm4ntr/incubator-airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,lyft/incubator-airflow,mtagle/airflow,apache/airflow,bolkedebruin/airflow,jgao54/airflow,Acehaidrey/incubator-airflow,bolkedebruin/airflow