Add missing includes.

Change-Id: I0737456e0221ebe9cc854d65c95a7d37d0869d56
diff --git a/install.cpp b/install.cpp
index 9db5640..31606bb 100644
--- a/install.cpp
+++ b/install.cpp
@@ -18,6 +18,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <limits.h>
+#include <string.h>
 #include <sys/stat.h>
 #include <sys/wait.h>
 #include <unistd.h>