Update pub credentials (#605)

Pub recently started requiring more OAuth2 scopes than our old
credentials held.

Author: nex3

pubspec.yaml

@@ -1,5 +1,5 @@
 name: sass
-version: 1.17.2-dev
+version: 1.17.2
 description: A Sass implementation in Dart.
 author: Dart Team <[email protected]>
 homepage: https://github.com/sass/dart-sass

tool/travis/credentials.tar.enc

@@ -5,8 +5,8 @@
 # Decrypts the encrypted credentials using Travis's private key and saves them
 # to credentials.tar.
 function decrypt_credentials() {
-    openssl aes-256-cbc -K $encrypted_d18df560dfb2_key \
-            -iv $encrypted_d18df560dfb2_iv \
+    openssl aes-256-cbc -K $encrypted_867f88017e77_key \
+            -iv $encrypted_867f88017e77_iv \
             -in tool/travis/credentials.tar.enc \
             -out credentials.tar -d
 }