feat: Replace the fnv hashmap by the hashbrown one

Cargo.toml

@@ -7,7 +7,7 @@ authors = ["Kerollmops <renault.cle@gmail.com>"]
 [dependencies]
 bincode = "1.0"
 byteorder = "1.2"
-fnv = "1.0"
+hashbrown = "0.1"
 lazy_static = "1.1"
 linked-hash-map = { version = "0.5", features = ["serde_impl"] }
 sdset = "0.3"

src/rank/distinct_map.rs

@@ -1,6 +1,7 @@
-use std::collections::HashMap;
 use std::hash::Hash;
 
+use hashbrown::HashMap;
+
 pub struct DistinctMap<K> {
     inner: HashMap<K, usize>,
     limit: usize,

src/rank/ranked_stream.rs

@@ -3,10 +3,10 @@ use std::{mem, vec, str};
 use std::error::Error;
 use std::hash::Hash;
 
-use fnv::FnvHashMap;
-use fst::Streamer;
-use group_by::GroupByMut;
 use ::rocksdb::rocksdb::{DB, Snapshot};
+use group_by::GroupByMut;
+use hashbrown::HashMap;
+use fst::Streamer;
 
 use crate::automaton::{self, DfaExt, AutomatonExt};
 use crate::rank::criterion::{self, Criterion};
@@ -77,7 +77,7 @@ where T: Deref<Target=DB>,
             op_builder.union()
         };
 
-        let mut matches = FnvHashMap::default();
+        let mut matches = HashMap::new();
 
         while let Some((input, indexed_values)) = stream.next() {
             for iv in indexed_values {