Fix compilation with gcc 8 (-Wstringop-truncation)

```
src/rpc.c: In function ‘dcc_r_sometoken_int’:
src/rpc.c:221:5: error: ‘strncpy’ output may be truncated copying 4
bytes from a string of length 12 [-Werror=stringop-truncation]
     strncpy(token, buf, 4);
     ^~~~~~~~~~~~~~~~~~~~~~
```

1 files changed, 1 insertions, 1 deletions

diff --git a/src/rpc.c b/src/rpc.c
index 56210d7..111b86a 100644
--- a/src/rpc.c
+++ b/src/rpc.c
@@ -218,7 +218,7 @@ int dcc_r_sometoken_int(int ifd, char *token, unsigned *val)
         return ret;
     }
 
-    strncpy(token, buf, 4);
+    memcpy(token, buf, 4);
     token[4] = '\0';
 
     buf[12] = '\0';             /* terminate */