bump version to 2.0.0

Author: hsbt

gdbm.gemspec

@@ -3,7 +3,7 @@
 
 Gem::Specification.new do |spec|
   spec.name          = "gdbm"
-  spec.version       = "2.0.0.beta1"
+  spec.version       = "2.0.0"
   spec.date          = '2017-04-28'
   spec.authors       = ["Yukihiro Matsumoto"]
   spec.email         = ["matz@ruby-lang.org"]