How can I extract the certificate from this pcap file?

With new versions of wireshark:

• Make sure the traffic is decoded as SSL, i.e. setup the SSL analyzer for this TCP stream in Analyze >> Decode As. Now it will show the SSL details for the packets.
• Pick the packet which contains the certificate, in this case packet 6.
• In the packet details expand Secure Socket Layer etc until you get to the certificate itself:

• Use the context menu (right click) and save the raw data of the certificate with Export Packet Bytes into a file, for example cert.der.
• With openssl x509 -inform der -in cert.der -text you can have a look at the certificate, with openssl x509 -inform der -in cert.der -outform pem -out cert.crt you can convert it into a PEM format (i.e. what you mean with crt format).