Rename build script to avoid conflict with bazel

It's difficult to include this repository using bazel, because
the file named "build" conflicts with new_go_repository generation
on case-insensitive filesystems (ref
https://github.com/bazelbuild/rules_go/issues/234). This change
renames the file to something that doesn't conflict, and also
renames the test script for consistency.

.travis.yml

@@ -38,9 +38,9 @@ install:
 script:
  - >
     if [ "${TARGET}" == "amd64" ]; then
-      GOARCH="${TARGET}" ./test;
+      GOARCH="${TARGET}" ./test.sh;
     else
-      GOARCH="${TARGET}" ./build;
+      GOARCH="${TARGET}" ./build.sh;
     fi
 
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