version 0.1.7 for bump to chrono 0.4.0

fixes #90
diff --git a/Cargo.toml b/Cargo.toml
index 1a0bbb9..71fe7e7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "tuf"
-version = "0.1.6"
+version = "0.1.7"
 authors = [ "heartsucker <heartsucker@autistici.org>" ]
 description = "Library for The Update Framework (TUF)"
 homepage = "https://github.com/heartsucker/rust-tuf"
@@ -30,7 +30,7 @@
 cli = [ "clap" ]
 
 [dependencies]
-chrono = { version = "0.3.1", features = [ "serde" ] }
+chrono = { version = "0.4", features = [ "serde" ] }
 clap = { version = "2.23", optional = true }
 data-encoding = "2.0.0-rc.1"
 env_logger = "0.4.3"
diff --git a/src/metadata.rs b/src/metadata.rs
index 7d77a93..6056b94 100644
--- a/src/metadata.rs
+++ b/src/metadata.rs
@@ -1,4 +1,5 @@
-use chrono::{DateTime, UTC};
+use chrono::DateTime;
+use chrono::offset::Utc;
 use data_encoding::HEXLOWER;
 use json;
 use pem;
@@ -133,14 +134,14 @@
 }
 
 pub trait Metadata<R: RoleType>: DeserializeOwned {
-    fn expires(&self) -> &DateTime<UTC>;
+    fn expires(&self) -> &DateTime<Utc>;
 }
 
 
 #[derive(Debug, PartialEq)]
 pub struct RootMetadata {
     consistent_snapshot: bool,
-    expires: DateTime<UTC>,
+    expires: DateTime<Utc>,
     pub version: i32,
     pub keys: HashMap<KeyId, Key>,
     pub root: RoleDefinition,
@@ -150,7 +151,7 @@
 }
 
 impl Metadata<Root> for RootMetadata {
-    fn expires(&self) -> &DateTime<UTC> {
+    fn expires(&self) -> &DateTime<Utc> {
         &self.expires
     }
 }
@@ -271,14 +272,14 @@
 
 #[derive(Debug, Clone)]
 pub struct TargetsMetadata {
-    expires: DateTime<UTC>,
+    expires: DateTime<Utc>,
     pub version: i32,
     pub delegations: Option<Delegations>,
     pub targets: HashMap<String, TargetInfo>,
 }
 
 impl Metadata<Targets> for TargetsMetadata {
-    fn expires(&self) -> &DateTime<UTC> {
+    fn expires(&self) -> &DateTime<Utc> {
         &self.expires
     }
 }
@@ -333,13 +334,13 @@
 
 #[derive(Debug)]
 pub struct TimestampMetadata {
-    expires: DateTime<UTC>,
+    expires: DateTime<Utc>,
     pub version: i32,
     pub meta: HashMap<String, MetadataMetadata>,
 }
 
 impl Metadata<Timestamp> for TimestampMetadata {
-    fn expires(&self) -> &DateTime<UTC> {
+    fn expires(&self) -> &DateTime<Utc> {
         &self.expires
     }
 }
@@ -381,13 +382,13 @@
 
 #[derive(Debug)]
 pub struct SnapshotMetadata {
-    expires: DateTime<UTC>,
+    expires: DateTime<Utc>,
     pub version: i32,
     pub meta: HashMap<String, SnapshotMetadataMetadata>,
 }
 
 impl Metadata<Snapshot> for SnapshotMetadata {
-    fn expires(&self) -> &DateTime<UTC> {
+    fn expires(&self) -> &DateTime<Utc> {
         &self.expires
     }
 }
diff --git a/src/tuf.rs b/src/tuf.rs
index 8b666e4..6dadb03 100644
--- a/src/tuf.rs
+++ b/src/tuf.rs
@@ -1,4 +1,4 @@
-use chrono::UTC;
+use chrono::offset::Utc;
 use json;
 use hyper::Url as HyperUrl;
 use hyper::client::Client;
@@ -217,7 +217,7 @@
 
         // handle the edge case where we never enter the update look
         // AND the first piece of metadata is expired
-        if temp_root.version == 1 && self.root.expires() <= &UTC::now() {
+        if temp_root.version == 1 && self.root.expires() <= &Utc::now() {
             return Err(Error::ExpiredMetadata(Role::Root));
         }
 
@@ -595,7 +595,7 @@
         Self::verify_meta::<R>(signed.clone(), role, threshold, trusted_ids, available_keys)?;
         let meta: M = json::from_value(signed.signed)?;
 
-        if !allow_expired && meta.expires() <= &UTC::now() {
+        if !allow_expired && meta.expires() <= &Utc::now() {
             return Err(Error::ExpiredMetadata(role.clone()));
         }