Fix invalid value for BigDecimal in Ruby 2.4.0+

[koic]

Fix https://github.com/kubo/ruby-oci8/issues/143 .

BigDecimal has changed that raise error for an invalid string for BigDecimal() in Ruby 2.4.0 RC1.

https://github.com/ruby/bigdecimal/commit/3081a627cebdc1fc119425c7a9f009dbb6bec8e8

Before (Ruby 2.3.3)

We can use both "1.E+00" and "1.0E+00" for BigDecimal().

require "bigdecimal"
BigDecimal("1.E+00").to_s #=> "0.1E1"
BigDecimal("1.E+00") == BigDecimal("1.0E+00") #=> true

After (Ruby 2.4.0 RC1)

We can not use "1.E+00" that will result ArgumentError.

require "bigdecimal"
BigDecimal("1.E+00") #=> ArgumentError: invalid value for BigDecimal(): "1.E+00"
BigDecimal("1.0E+00") #=> 0.1e1

This PR has change below.

Previously used format of to_char:

OraNumber(1).to_char('FM9.99999999999999999999999999999999999999EEEE') #=> "1.E+00"

This PR used format of to_char:

OraNumber(1).to_char('FM9.09999999999999999999999999999999999999EEEE') #=> "1.0E+00"

See also, I'm asking questions about BigDecimal() change.

https://github.com/ruby/bigdecimal/issues/47 .

By the way, I think that this PR change using "1.0E+00" is better, maybe.

Related issue: https://github.com/rsim/oracle-enhanced/issues/1085

Thanks.

[yahonda]

Confirmed this pull request addresses this issue and rsim/oracle-enhanced#1085 . Thanks.

[kubo]

@koic Thanks a lot!

[koic]

Thanks for merging.