Fix anyhow dependency issues (#208)

- Do not require backtrace feature
- Starting version 1.0.77, anyhow gathers backtrace is std feature (enabled by default)
  is specified even if backtrace feature is not enabled.
  Therefore specify default features as false.
- Specify version 1.0.45 since that is the minimul version required to successfully
  compile regorus

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

src/builtins/semver.rs

@@ -12,7 +12,7 @@ use semver::Version;
 use std::cmp::Ordering;
 use std::collections::HashMap;
 
-use anyhow::{Ok, Result};
+use anyhow::Result;
 
 pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
     m.insert("semver.compare", (compare, 2));

src/builtins/uuid.rs

@@ -9,7 +9,7 @@ use crate::value::Value;
 
 use std::collections::{BTreeMap, HashMap};
 
-use anyhow::{Ok, Result};
+use anyhow::Result;
 use uuid::{Timestamp, Uuid};
 
 pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {