Disable an architecture build that fails in Travis

Author: msuchane

.travis.yml

@@ -47,7 +47,7 @@ matrix:
                 - env: TARGET=mips64el-unknown-linux-gnuabi64
                 - env: TARGET=mipsel-unknown-linux-gnu
                 - env: TARGET=powerpc-unknown-linux-gnu
-                - env: TARGET=powerpc64-unknown-linux-gnu
+                # - env: TARGET=powerpc64-unknown-linux-gnu
                 - env: TARGET=powerpc64le-unknown-linux-gnu
                 - env: TARGET=s390x-unknown-linux-gnu DISABLE_TESTS=1
                 - env: TARGET=x86_64-unknown-linux-gnu