message: Fix tests on Node 8.
  The exception class name is not in the message anymore. I guess that's what `code` is for.
diff: @@ -389,7 +389,7 @@ suite('Project Config', () => {
  assert.throws(
  () => config.validate(),
  - /AssertionError: Polymer Config Error: a "fragments" path \(.*bar.html\) does not resolve within root \(.*public\)/);
  + /Polymer Config Error: a "fragments" path \(.*bar.html\) does not resolve within root \(.*public\)/);
  });
  test('throws an exception when entrypoint does not resolve within root', () => {
  @@ -402,7 +402,7 @@ suite('Project Config', () => {
  assert.throws(
  () => config.validate(),
  - /AssertionError: Polymer Config Error: entrypoint \(.*bar.html\) does not resolve within root \(.*public\)/);
  + /Polymer Config Error: entrypoint \(.*bar.html\) does not resolve within root \(.*public\)/);
  });
  test('throws an exception when shell does not resolve within root', () => {
  @@ -415,7 +415,7 @@ suite('Project Config', () => {
  assert.throws(
  () => config.validate(),
  - /AssertionError: Polymer Config Error: shell \(.*bar.html\) does not resolve within root \(.*public\)/);
  + /Polymer Config Error: shell \(.*bar.html\) does not resolve within root \(.*public\)/);
  });
  test('returns true when a single, unnamed build is defined', () => {
  @@ -444,7 +444,7 @@ suite('Project Config', () => {
  });
  assert.throws(
  () => config.validate(),
  - 'AssertionError: Polymer Config Error: "builds" ([object Object]) expected an array of build configurations.');
  + 'Polymer Config Error: "builds" ([object Object]) expected an array of build configurations.');
  });
  test('throws an exception when builds array contains duplicate names', () => {
  @@ -463,7 +463,7 @@ suite('Project Config', () => {
  });
  assert.throws(
  () => config.validate(),
  - 'AssertionError: Polymer Config Error: "builds" duplicate build name "bundled" found. Build names must be unique.');
  + 'Polymer Config Error: "builds" duplicate build name "bundled" found. Build names must be unique.');
  });
  test('throws an exception when builds array contains an unnamed build', () => {
  @@ -481,7 +481,7 @@ suite('Project Config', () => {
  });
  assert.throws(
  () => config.validate(),
  - 'AssertionError: Polymer Config Error: all "builds" require a "name" property when there are multiple builds defined.');
  + 'Polymer Config Error: all "builds" require a "name" property when there are multiple builds defined.');
  });
  test('throws an exception when builds array contains an invalid preset', () => {
  @@ -498,7 +498,7 @@ suite('Project Config', () => {
  });
  assert.throws(
  () => config.validate(),
  - 'AssertionError: Polymer Config Error: "not-a-real-preset" is not a valid "builds" preset.');
  + 'Polymer Config Error: "not-a-real-preset" is not a valid "builds" preset.');
  });
  });
  