fix: split ALTER TABLE into separate ADD COLUMN statements in migration 0002

SQLite does not support adding multiple columns in a single ALTER TABLE
statement. The previous migration tried to add 6 columns at once and
caused a syntax error, crashing the service at startup.

Bump VERSION 0.1.7 -> 0.1.8

Makefile

@@ -1,5 +1,5 @@
 BINARY=nasctl
-VERSION?=0.1.7
+VERSION?=0.1.8
 GO?=go
 LDFLAGS=-s -w -X github.com/darroyo/nasctl/internal/web.Version=$(VERSION) -X github.com/darroyo/nasctl/internal/web.Commit=$(shell git rev-parse --short HEAD 2>/dev/null || echo unknown)
 BUILD_FLAGS=CGO_ENABLED=0