fix(section-4): update typos and grammar

[sevillaarvin]

index

• remove redundant word consider

lesson-21

• change get-input-uom to get-input-unit
• add missing article a
• add missing word apply

lesson-22

• update typo cleat to clear

lesosn-23

• add missing s for plural function

lesson-24

• move misplaced comma
• update typo is to in
• update typo out to our
• update typo the to they
• change word channels to functions

lesson-26

• add missing period
• add missing s
• change word the to when
• change render-header to init-header
• change header.cljs path from state to chat
• update typo DOME to DOM
• add missing namespace learn-cljs
• add missing apply to dom/with-children call with vector argument
• add msg-ch argument to init-composer call
• specify subdirectory of api.cljs
• remove .core submodule
• update typo Clojure Script to ClojureScript