Nudge libcurl due to MacOS 10.13 build issue

Ref: https://github.com/VCVRack/Rack/issues/122

dep/Makefile

@@ -98,13 +98,13 @@ $(libsamplerate):
 	$(MAKE) -C libsamplerate-0.1.9/src install
 
 $(libcurl):
-	$(WGET) https://github.com/curl/curl/files/1101227/curl-7.54.1.tar.gz
-	$(UNTAR) curl-7.54.1.tar.gz
-	cd curl-7.54.1 && ./configure --prefix="$(LOCAL)" \
+	$(WGET) https://github.com/curl/curl/files/1101227/curl-7.56.0.tar.gz
+	$(UNTAR) curl-7.56.0.tar.gz
+	cd curl-7.56.0 && ./configure --prefix="$(LOCAL)" \
 		--disable-ftp --disable-file --disable-ldap --disable-ldaps --disable-rtsp --disable-proxy --disable-dict --disable-telnet --disable-tftp --disable-pop3 --disable-imap --disable-smb --disable-smtp --disable-gopher --disable-manual \
 		--without-zlib --without-ssl --without-ca-bundle --without-ca-path --without-ca-fallback --without-libpsl --without-libmetalink --without-libssh2 --without-librtmp --without-winidn --without-libidn2 --without-nghttp2
-	$(MAKE) -C curl-7.54.1
-	$(MAKE) -C curl-7.54.1 install
+	$(MAKE) -C curl-7.56.0
+	$(MAKE) -C curl-7.56.0 install
 
 $(libzip):
 	$(WGET) https://nih.at/libzip/libzip-1.2.0.tar.gz