Fix spelling errors in core-principles.md #1055

Job	Run time
test	5m 44s
cli-test	6m 30s
check	4m 12s
e2e-example-test (basic, core)	8m 41s
e2e-example-test (capsules, core)	9m 41s
e2e-example-test (custom_server, core)	5m 38s
e2e-example-test (error_views, core)	8m 12s
e2e-example-test (freezing_and_thawing, core)	8m 17s
e2e-example-test (global_state, core)	8m 0s
e2e-example-test (helper_build_state, core)	8m 42s
e2e-example-test (i18n, core)	7m 39s
e2e-example-test (idb_freezing, core)	8m 19s
e2e-example-test (index_view, core)	8m 22s
e2e-example-test (js_interop, core)	8m 6s
e2e-example-test (plugins, core)	8m 45s
e2e-example-test (preload, core)	7m 34s
e2e-example-test (router_state, core)	6m 39s
e2e-example-test (rx_state, core)	8m 20s
e2e-example-test (set_headers, core)	8m 26s
e2e-example-test (state_generation, core)	10m 55s
e2e-example-test (static_content, core)	7m 46s
e2e-example-test (suspense, core)	7m 18s
e2e-example-test (unreactive, core)	6m 26s
	2h 58m 12s

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