update lab1-8 codes and docs. now version is 0.2

code/lab7/user/libs/syscall.c

@@ -70,7 +70,7 @@ sys_pgdir(void) {
     return syscall(SYS_pgdir);
 }
 
-size_t
+int
 sys_gettime(void) {
     return syscall(SYS_gettime);
 }