Spelling fixes I noticed

acieved -> achieved
occured -> occurred
occurence -> occurrence
convinence -> convenience
primarky -> primary
whis -> which
concated -> concatenated
Merge pull request #1140 from ehershey/patch-1

Spelling fixes I noticed
Update gridfs.md

correct exemple of seek
Merge pull request #1144 from benzen/patch-1

Update gridfs.md