deps: bump regex-syntax to 0.6.6

0.6.6 introduced a new API that regex now uses, so it is the new
required minimal version.

Fixes #570

CHANGELOG.md

@@ -1,3 +1,17 @@
+1.1.5 (2019-04-01)
+==================
+This releases fixes a bug in regex's dependency specification where it requires
+a newer version of regex-syntax, but this wasn't communicated correctly in the
+Cargo.toml. This would have been caught by a minimal version check, but this
+check was disabled because the `rand` crate itself advertises incorrect
+dependency specifications.
+
+Bug fixes:
+
+* [BUG #570](https://github.com/rust-lang/regex/pull/570):
+  Fix regex-syntax minimal version.
+
+
 1.1.4 (2019-03-31)
 ==================
 This release fixes a backwards compatibility regression where Regex was no

Cargo.toml

@@ -32,7 +32,7 @@ memchr = "2.0.2"
 # For managing regex caches quickly across multiple threads.
 thread_local = "0.3.6"
 # For parsing regular expressions.
-regex-syntax = { path = "regex-syntax", version = "0.6.2" }
+regex-syntax = { path = "regex-syntax", version = "0.6.6" }
 # For compiling UTF-8 decoding into automata.
 utf8-ranges = "1.0.1"