deps: Upgrade github.com/gohugoio/hashstructure from 0.1.0 to 0.3.0

Faster hashing of maps:

```
           │ stash.bench  │      deps-hashstructv030.bench      │
           │    sec/op    │    sec/op     vs base               │
HashMap-10   198.9µ ± ∞ ¹   142.6µ ± ∞ ¹  -28.31% (p=0.029 n=4)
¹ need >= 6 samples for confidence interval at level 0.95

           │  stash.bench  │      deps-hashstructv030.bench       │
           │     B/op      │     B/op       vs base               │
HashMap-10   92.38Ki ± ∞ ¹   37.14Ki ± ∞ ¹  -59.80% (p=0.029 n=4)
¹ need >= 6 samples for confidence interval at level 0.95

           │ stash.bench  │      deps-hashstructv030.bench      │
           │  allocs/op   │  allocs/op    vs base               │
HashMap-10   6.747k ± ∞ ¹   4.748k ± ∞ ¹  -29.63% (p=0.029 n=4)
```

common/hashing/hashing_test.go

@@ -142,3 +142,16 @@ func BenchmarkHashString(b *testing.B) {
 		})
 	}
 }
+
+func BenchmarkHashMap(b *testing.B) {
+	m := map[string]interface{}{}
+	for i := 0; i < 1000; i++ {
+		m[fmt.Sprintf("key%d", i)] = i
+	}
+
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		HashString(m)
+	}
+}