Improve the npm dependency caching strategy on Travis CI

[johnbillion]

See [44989]. Caching $HOME/.npm instead of node_modules is preferable because the latter can cause issues if the cached modules were compiled using a newer version of node. This situation can occur when Travis falls back to the default branch cache.

[johnbillion]

In 44993:

Build/Test tools: Switch npm dependency caching strategy on Travis CI.

This switches to caching npm's local cache instead of node_modules in order to prevent issues caused by modules compiled using a different version of node.

See #46632

[johnbillion]

In 44994:

Build/Test tools: Switch npm dependency caching strategy on Travis CI.

This switches to caching npm's local cache instead of node_modules in order to prevent issues caused by modules compiled using a different version of node.

Merges [44993] into the 5.1 branch.

See #46632

[johnbillion]

In 44995:

Build/Test tools: Switch npm dependency caching strategy on Travis CI.

This switches to caching npm's local cache instead of node_modules in order to prevent issues caused by modules compiled using a different version of node.

Merges [44993] into the 5.0 branch.

See #46632

[johnbillion]

In 44996:

Build/Test tools: Switch npm dependency caching strategy on Travis CI.

This switches to caching npm's local cache instead of node_modules in order to prevent issues caused by modules compiled using a different version of node.

Merges [44993] into the 4.9 branch.

See #46632

[johnbillion]

In 44997:

Build/Test tools: Switch npm dependency caching strategy on Travis CI.

This switches to caching npm's local cache instead of node_modules in order to prevent issues caused by modules compiled using a different version of node.

Merges [44993] into the 4.8 branch.

See #46632

[johnbillion]

In 44998:

Build/Test tools: Switch npm dependency caching strategy on Travis CI.

This switches to caching npm's local cache instead of node_modules in order to prevent issues caused by modules compiled using a different version of node.

Merges [44993] into the 4.7 branch.

See #46632

[johnbillion]

In 44999:

Build/Test tools: Switch npm dependency caching strategy on Travis CI.

This switches to caching npm's local cache instead of node_modules in order to prevent issues caused by modules compiled using a different version of node.

Merges [44993] into the 4.6 branch.

See #46632

[johnbillion]

In 45000:

Build/Test tools: Switch npm dependency caching strategy on Travis CI.

This switches to caching npm's local cache instead of node_modules in order to prevent issues caused by modules compiled using a different version of node.

Merges [44993] into the 4.5 branch.

See #46632

[johnbillion]

In 45001:

Build/Test tools: Switch npm dependency caching strategy on Travis CI.

This switches to caching npm's local cache instead of node_modules in order to prevent issues caused by modules compiled using a different version of node.

Merges [44993] into the 4.4 branch.

See #46632

[johnbillion]

In 45002:

Build/Test tools: Switch npm dependency caching strategy on Travis CI.

This switches to caching npm's local cache instead of node_modules in order to prevent issues caused by modules compiled using a different version of node.

Merges [44993] into the 4.1 branch.

See #46632

[johnbillion]

In 45003:

Build/Test tools: Switch npm dependency caching strategy on Travis CI.

This switches to caching npm's local cache instead of node_modules in order to prevent issues caused by modules compiled using a different version of node.

Merges [44993] into the 4.0 branch.

See #46632