Update pycall version

Author: mrkn

matplotlib.gemspec

@@ -21,7 +21,7 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
-  spec.add_dependency "pycall", ">= 0.1.0.alpha.20170419b"
+  spec.add_dependency "pycall", ">= 0.1.0.alpha.20170426"
 
   spec.add_development_dependency "bundler", "~> 1.13"
   spec.add_development_dependency "rake", "~> 10.0"