Merge branch 'master' into dev

* master:
  Cover Ruby 2.6 on travis and appveyor
  Rewrite unix fork reopen to be compatible with ruby 2.6

.travis.yml

@@ -8,6 +8,7 @@ rvm:
   - 2.3
   - 2.4
   - 2.5
+  - 2.6
   - ruby-head
 
 sudo: false

appveyor.yml

@@ -20,6 +20,12 @@ environment:
     - CHILDPROCESS_POSIX_SPAWN: false
       CHILDPROCESS_UNSET: should-be-unset
       RUBY_VERSION: 25-x64
+    - CHILDPROCESS_POSIX_SPAWN: true
+      CHILDPROCESS_UNSET: should-be-unset
+      RUBY_VERSION: 26-x64
+    - CHILDPROCESS_POSIX_SPAWN: false
+      CHILDPROCESS_UNSET: should-be-unset
+      RUBY_VERSION: 26-x64
 
 install:
   - set PATH=C:\Ruby%RUBY_VERSION%\bin;%PATH%

lib/childprocess/unix/fork_exec_process.rb

@@ -29,8 +29,16 @@ def launch_process
           exec_r.close
           set_env
 
-          STDOUT.reopen(stdout || "/dev/null")
-          STDERR.reopen(stderr || "/dev/null")
+          if stdout
+            STDOUT.reopen(stdout)
+          else
+            STDOUT.reopen("/dev/null", "a+")
+          end
+          if stderr
+            STDERR.reopen(stderr)
+          else
+            STDERR.reopen("/dev/null", "a+")
+          end
 
           if duplex?
             STDIN.reopen(reader)