Upgrade mips64 to Tier 1

Author: Susurrus

README.md

@@ -62,6 +62,8 @@ Tier 1:
   * powerpc64-unknown-linux-gnu
   * powerpc64le-unknown-linux-gnu
   * mips-unknown-linux-gnu
+  * mips64-unknown-linux-gnuabi64
+  * mips64el-unknown-linux-gnuabi64
   * mipsel-unknown-linux-gnu
   * i686-unknown-linux-musl
   * x86_64-unknown-linux-musl
@@ -74,8 +76,6 @@ Tier 2:
   * arm-unknown-linux-musleabi (requires Rust >= 1.14)
   * armv7-linux-androideabi
   * i686-linux-android (requires Rust >= 1.18)
-  * mips64-unknown-linux-gnuabi64
-  * mips64el-unknown-linux-gnuabi64
   * s390x-unknown-linux-gnu
   * x86_64-linux-android (requires Rust >= 1.18)