Enable TextClause values for server_default

gistfile1.py

# Test Models.py
class Test(Base):
    __tablename__ = 'test'
    
    id = Column(BigInteger, primary_key=True)
    created_at = Column(DateTime, server_default=text('now()'))
    created_at2 = Column(DateTime, server_default=text("(now() at time zone 'utc')"))
    created_at3 = Column(DateTime, server_default=func.now())
    
###
### Current master version autogenerated this:
###
def upgrade():
    op.create_table('test',
    sa.Column('id', sa.BigInteger(), nullable=False),
    sa.Column('created_at', sa.DateTime(), server_default='now()', nullable=True),
    sa.Column('created_at2', sa.DateTime(), server_default="(now() at time zone 'utc')", nullable=True),
    sa.Column('created_at3', sa.DateTime(), server_default='now()', nullable=True),
    sa.PrimaryKeyConstraint('id')
    )
    
    
###
### My fix autogenerated this:
###
def upgrade():
    op.create_table('test',
    sa.Column('id', sa.BigInteger(), nullable=False),
    sa.Column('created_at', sa.DateTime(), server_default=sa.text('now()'), nullable=True),
    sa.Column('created_at2', sa.DateTime(), server_default=sa.text("(now() at time zone 'utc')"), nullable=True),
    sa.Column('created_at3', sa.DateTime(), server_default='now()', nullable=True),
    sa.PrimaryKeyConstraint('id')
    )