doc: standardizing on make -j4

Standardizes docs to use -j4 instead of -j8 as it appears to be the
most inclusive recommendation based on discussion in
nodejs#9961.

.github/PULL_REQUEST_TEMPLATE.md

@@ -9,7 +9,7 @@ Contributors guide: https://github.com/nodejs/node/blob/master/CONTRIBUTING.md
 ##### Checklist
 <!-- Remove items that do not apply. For completed items, change [ ] to [x]. -->
 
-- [ ] `make -j8 test` (UNIX), or `vcbuild test nosign` (Windows) passes
+- [ ] `make -j4 test` (UNIX), or `vcbuild test nosign` (Windows) passes
 - [ ] tests and/or benchmarks are included
 - [ ] documentation is changed or added
 - [ ] commit message follows commit guidelines

CONTRIBUTING.md

@@ -156,7 +156,7 @@ to see how they should be structured can also help.
 To run the tests on Unix / OS X:
 
 ```text
-$ ./configure && make -j8 test
+$ ./configure && make -j4 test
 ```
 
 Windows:
@@ -189,7 +189,7 @@ You can run tests directly with node:
 $ ./node ./test/parallel/test-stream2-transform.js
 ```
 
-Remember to recompile with `make -j8` in between test runs if you change
+Remember to recompile with `make -j4` in between test runs if you change
 core modules.
 
 ### Step 6: Push

doc/guides/building-node-with-ninja.md

@@ -16,7 +16,7 @@ ninja: Entering directory `out/Release`
 
 The bottom line will change while building, showing the progress as `[finished/total]` build steps.
 This is useful output that `make` does not produce and is one of the benefits of using Ninja.
-Also, Ninja will likely compile much faster than even `make -j8` (or `-j<number of processor threads on your machine>`).
+Also, Ninja will likely compile much faster than even `make -j4` (or `-j<number of processor threads on your machine>`).
 
 ## Considerations
 

doc/onboarding-extras.md

@@ -70,7 +70,7 @@ Please use these when possible / appropriate
   * major vs. everything else: run last versions tests against this version, if they pass, **probably** minor or patch
   * A breaking change helper ([full source](https://gist.github.com/chrisdickinson/ba532fa0e4e243fb7b44)):
   ```sh
-  git checkout $(git show -s --pretty='%T' $(git show-ref -d $(git describe --abbrev=0) | tail -n1 | awk '{print $1}')) -- test; make -j8 test
+  git checkout $(git show -s --pretty='%T' $(git show-ref -d $(git describe --abbrev=0) | tail -n1 | awk '{print $1}')) -- test; make -j4 test
   ```
 
 

doc/onboarding.md

@@ -186,7 +186,7 @@ Landing a PR
   * If `git am` fails, see [the relevant section of the Onboarding Extras doc](./onboarding-extras.md#if-git-am-fails).
 * `git rebase -i upstream/master`
 * Squash into logical commits if necessary.
-* `./configure && make -j8 test` (`-j8` builds node in parallel with 8 threads. adjust to the number of cores (or processor-level threads) your processor has (or slightly more) for best results.)
+* `./configure && make -j4 test` (`-j4` builds node in parallel with 4 threads. adjust to the number of cores (or processor-level threads) your processor has (or slightly more) for best results.)
 * Amend the commit description.
   * The commit message text must conform to the [commit message guidelines](../CONTRIBUTING.md#step-3-commit).
   * Add required metadata: