Increase default max memory size

For now, increase to the max supported by sqlite3_malloc64(), as per
https://sqlite.org/forum/forumpost/b1ba232667130afa?t=h.

Author: otoolep

sqlite3.go

@@ -23,6 +23,7 @@ package sqlite3
 #cgo CFLAGS: -DSQLITE_OMIT_SHARED_CACHE
 #cgo CFLAGS: -DSQLITE_ENABLE_JSON1
 #cgo CFLAGS: -DSQLITE_ENABLE_DBSTAT_VTAB
+#cgo CFLAGS: -DSQLITE_MEMDB_DEFAULT_MAXSIZE=2147483648
 #cgo CFLAGS: -Wno-deprecated-declarations
 #cgo linux,!android CFLAGS: -DHAVE_PREAD64=1 -DHAVE_PWRITE64=1
 #ifndef USE_LIBSQLITE3