patch 8.0.1744: on some systems /dev/stdout isn't writable

Problem:    On some systems /dev/stdout isn't writable.
Solution:   Skip test if writing is not possible. (James McCoy, closes #2830)
diff --git a/src/testdir/test_writefile.vim b/src/testdir/test_writefile.vim
index b8e0001..672ddd3 100644
--- a/src/testdir/test_writefile.vim
+++ b/src/testdir/test_writefile.vim
@@ -105,6 +105,10 @@
   if !has('unix')
     return
   endif
-  " Just check that this doesn't cause an error.
-  call writefile(['one'], '/dev/stdout')
+  if filewritable('/dev/stdout')
+    " Just check that this doesn't cause an error.
+    call writefile(['one'], '/dev/stdout')
+  else
+    throw 'Skipped: /dev/stdout is not writable'
+  endif
 endfunc
diff --git a/src/version.c b/src/version.c
index 52486ac..0c25fd7 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1744,
+/**/
     1743,
 /**/
     1742,