[wealth_dynamics] Update lecture to comply with QuantEcon style guide (titles)

[mmcky]

I would like to review lectures/wealth_dynamics for the following quantecon style guide rule

Please review the following rules

  # Title Rules
  qe-title-001:
    title: "Lecture Titles"
    category: "titles"
    type: "capitalization"
    priority: "mandatory"
    rule: "Capitalize ALL words in lecture titles."
    examples:
      correct: "How it Works: Data, Variables and Names"
      incorrect: "How it works: data, variables and names"
      
  qe-title-002:
    title: "Section/Subsection Headings"
    category: "titles"
    type: "capitalization"
    priority: "mandatory"
    rule: "Capitalize ONLY the first word and proper nouns in all other headings (sections, subsections, etc.)."
    examples:
      correct: 
        - "Binary packages with Python frontends"
        - "Adding a new reference to QuantEcon"
      incorrect: "Binary Packages with Python Frontends"

Then check the lecture to ensure compliance.