Upgrade rust/crates/regex-syntax to 0.6.18

Test: None
Change-Id: Ibb0a5495aac0d848e661ddd70f729a76b949248f
diff --git a/src/lib.rs b/src/lib.rs
index e9f59d8..7892668 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -175,7 +175,7 @@
 /// The string returned may be safely used as a literal in a regular
 /// expression.
 pub fn escape(text: &str) -> String {
-    let mut quoted = String::with_capacity(text.len());
+    let mut quoted = String::new();
     escape_into(text, &mut quoted);
     quoted
 }
@@ -185,6 +185,7 @@
 /// This will append escape characters into the given buffer. The characters
 /// that are appended are safe to use as a literal in a regular expression.
 pub fn escape_into(text: &str, buf: &mut String) {
+    buf.reserve(text.len());
     for c in text.chars() {
         if is_meta_character(c) {
             buf.push('\\');