Issue type:

[ ] question
[x] bug report
[ ] feature request
[ ] documentation issue

Database system/driver:

[ ] cordova
[ ] mongodb
[ ] mssql
[ ] mysql / mariadb
[ ] oracle
[x ] postgres
[ ] sqlite
[ ] sqljs
[ ] react-native
[ ] expo

TypeORM version:

[ ] latest
[ ] @next
[x] 0.2.11 (or put your version here)

Steps to reproduce or a small repository showing the problem:

I apologize- I can't help but think I've seen a similar issue but I couldn't find it in opened or closed issues.

Let's say I have a varchar column with length of 50;

@Column({
   length: 50
})
public example: string;

Which results in this migration:

CREATE TABLE "bug" ("text" character varying(50))

And then I go ahead and change the length to 51;

@Column({
   length: 51
})
public example: string;

The resulting generated migration code is:

ALTER TABLE "bug" DROP COLUMN "example"
ALTER TABLE "bug" ADD "example" character varying(51)

Which obviously would result in data loss.
I would have expected;

ALTER TABLE "bug" ALTER COLUMN "example" character varying(51)

I did see something in #3352 which I think could be related? Although its for schema sync.