Change single-quoting of floats in PostgreSQL compare_server_default

Change single-quoting of floats in PostgreSQL compare_server_default

Do not wrap string defaults with single quotes when comparing against
columns of type float or numeric.
This fixes the crash occuring when the default of a float column is
an integer value (e.g., DEFAULT 5), while the Python server_default is
a string (e.g., server_default="5.0"). This results in the query
used in the comparison to throw a DataError ('SELECT 5 = '5.0').