Fix using schleuder 3.x with ruby 2.7.
Explicitly depend on BigDecimal 1.4, because later versions are incompatible with activesupport 4.2, which is a dependency of activerecord 4.2.
Explicitly depend on BigDecimal 1.4, because later versions are incompatible with activesupport 4.2, which is a dependency of activerecord 4.2.