Change build env reference

tutorials/http/http-proxy-client/Makefile

@@ -6,7 +6,7 @@ OUT ?= -o $(PROG)                 # Compiler argument for output file
 SOURCES = main.c $(REPO_ROOT)/mongoose.c  packed_fs.c      # Source code files, packed_fs.c contains ca.pem, which contains CA certs for TLS
 CFLAGS = -I$(REPO_ROOT) -W -Wall -Wextra -g -I.  # Build options
 
-# Mongoose build options. See https://mongoose.ws/documentation/#build-options
+# Mongoose build options. See https://mongoose.ws/docs/getting-started/build-environment/
 CFLAGS_MONGOOSE += -DMG_ENABLE_LINES=1
 
 # See tutorial at https://mongoose.ws/tutorials/http-proxy-client/