Update stringio to 3.1.4

This updates stringio to 3.1.4, which includes all the fixes from
ruby/stringio#116. All CRuby tests and ruby/spec specs for stringio
are now green.

Tests are from v3.1.4 of the ruby/stringio repo.

Author: headius

lib/pom.rb

@@ -97,7 +97,7 @@ def log(message=nil)
     # ['set', '1.0.2'],
     ['shellwords', '0.1.0'],
     ['singleton', '0.1.1'],
-    ['stringio', '3.1.2'],
+    ['stringio', '3.1.4'],
     ['strscan', '3.1.0'],
     ['subspawn', '0.1.1'], # has 3 transitive deps:
       ['subspawn-posix', '0.1.1'],

lib/pom.xml

@@ -749,7 +749,7 @@ DO NOT MODIFY - GENERATED CODE
     <dependency>
       <groupId>rubygems</groupId>
       <artifactId>stringio</artifactId>
-      <version>3.1.2</version>
+      <version>3.1.4</version>
       <type>gem</type>
       <scope>provided</scope>
       <exclusions>
@@ -1147,7 +1147,7 @@ DO NOT MODIFY - GENERATED CODE
           <include>specifications/securerandom-0.2.0*</include>
           <include>specifications/shellwords-0.1.0*</include>
           <include>specifications/singleton-0.1.1*</include>
-          <include>specifications/stringio-3.1.2*</include>
+          <include>specifications/stringio-3.1.4*</include>
           <include>specifications/strscan-3.1.0*</include>
           <include>specifications/subspawn-0.1.1*</include>
           <include>specifications/subspawn-posix-0.1.1*</include>
@@ -1227,7 +1227,7 @@ DO NOT MODIFY - GENERATED CODE
           <include>gems/securerandom-0.2.0*/**/*</include>
           <include>gems/shellwords-0.1.0*/**/*</include>
           <include>gems/singleton-0.1.1*/**/*</include>
-          <include>gems/stringio-3.1.2*/**/*</include>
+          <include>gems/stringio-3.1.4*/**/*</include>
           <include>gems/strscan-3.1.0*/**/*</include>
           <include>gems/subspawn-0.1.1*/**/*</include>
           <include>gems/subspawn-posix-0.1.1*/**/*</include>
@@ -1307,7 +1307,7 @@ DO NOT MODIFY - GENERATED CODE
           <include>cache/securerandom-0.2.0*</include>
           <include>cache/shellwords-0.1.0*</include>
           <include>cache/singleton-0.1.1*</include>
-          <include>cache/stringio-3.1.2*</include>
+          <include>cache/stringio-3.1.4*</include>
           <include>cache/strscan-3.1.0*</include>
           <include>cache/subspawn-0.1.1*</include>
           <include>cache/subspawn-posix-0.1.1*</include>

test/mri/stringio/test_ractor.rb

@@ -11,7 +11,7 @@ def test_ractor
       require "stringio"
       $VERBOSE = nil
       r = Ractor.new do
-        io = StringIO.new("")
+        io = StringIO.new(+"")
         io.puts "abc"
         io.truncate(0)
         io.puts "def"