Do not declare variable in for loop

Caused build failure in Travis (due to lack of C99 mode):

sbox.c: In function ‘sbox_run_v’:

sbox.c:185:3: error: ‘for’ loop initial declarations are only allowed in C99 mode

   for (int i = 3; i < max; i++)

   ^

sbox.c:185:3: note: use option -std=c99 or -std=gnu99 to compile your code

1 files changed, 2 insertions, 1 deletions

diff --git a/src/firejail/sbox.c b/src/firejail/sbox.c
index 9e4cd1da9..203c0fc03 100644
--- a/src/firejail/sbox.c
+++ b/src/firejail/sbox.c
@@ -182,7 +182,8 @@ int sbox_run_v(unsigned filtermask, char * const arg[]) {
 
                 // close all other file descriptors
                 int max = 20; // getdtablesize() is overkill for a firejail process
-                for (int i = 3; i < max; i++)
+                int i = 3;
+                for (i = 3; i < max; i++)
                         close(i); // close open files
 
                 umask(027);