fix lower case warnings on Dockerfile

[tomich]

Avoid warnings during Dockerfile builds by using upper case on FROM and AS statements.

Will remove following warnings from docker build:

WARN: FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 1) 0.0s => WARN: FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 6) 0.0s => WARN: FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 16) 0.0s => WARN: FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 21) 0.0s => WARN: FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 29) 0.0s