add LinearAlgebra to deps

[ctarn]

Colors.jl use LinearAlgebra, but doesn't include it in deps.

It would cause an error when using PackageCompiler.jl. The error message is:

ERROR: LoadError: MethodError: no method matching inv(::Matrix{Float64})
The function `inv` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  inv(::ComplexF64)
   @ Base complex.jl:479
  inv(::BigFloat)
   @ Base mpfr.jl:678
  inv(::Missing)
   @ Base missing.jl:101
  ...

Stacktrace:
 [1] top-level scope
   @ ~/.julia/packages/Colors/VFEJ1/src/conversions.jl:616
 [2] top-level scope
   @ ~/.julia/packages/Colors/VFEJ1/src/Colors.jl:30
 [3] top-level scope
   @ stdin:5

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.67%. Comparing base (b656cf7) to head (c7f9bd8).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #576      +/-   ##
==========================================
- Coverage   96.75%   96.67%   -0.09%     
==========================================
  Files           9        9              
  Lines        1296     1262      -34     
==========================================
- Hits         1254     1220      -34     
  Misses         42       42              

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