install.sh: Put standard PATH directories in front

Apparently some people are getting xattr shipped with Python.framework
in front of the system xattr, and that breaks the stub. Let's make sure
nothing overrides standard system binaries.

Fixes: #30
Signed-off-by: Hector Martin <marcan@marcan.st>

src/install.sh

@@ -10,7 +10,7 @@ export DYLD_LIBRARY_PATH=$PWD/Frameworks/Python.framework/Versions/Current/lib
 export DYLD_FRAMEWORK_PATH=$PWD/Frameworks
 python=Frameworks/Python.framework/Versions/3.9/bin/python3.9
 export SSL_CERT_FILE=$PWD/Frameworks/Python.framework/Versions/Current/etc/openssl/cert.pem
-export PATH="$PWD/bin:$PATH"
+export PATH="$PWD/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:$PATH"
 
 arch=