fix Program from sh_string_type

[Tuebel]

Compiling shader programs as described in https://github.com/JuliaGL/GLAbstraction.jl/blob/master/example/drawing_polygons_with_GLAbstraction.jl via GLA.frag and Program(sh_string_type...) gave me an Error:

MethodError: no method matching GLAbstraction.Shader(::Tuple{UInt32, String})

I think the method broke here: a6076c8#diff-8728a176445e31cf3b9dc440a8dd9fd201f9aa51f761e51115ff058ffb408a11R76

Unpacking the tuple as argument for the Shader fixed it.

[codecov-commenter]

Codecov Report

Merging #103 (dd550ca) into master (534f6f9) will decrease coverage by 1.28%.
The diff coverage is 29.80%.

@@            Coverage Diff             @@
##           master     #103      +/-   ##
==========================================
- Coverage   34.17%   32.89%   -1.29%     
==========================================
  Files          15       15              
  Lines        1308     1356      +48     
==========================================
- Hits          447      446       -1     
- Misses        861      910      +49     

Impacted Files	Coverage Δ
src/GLAbstraction.jl	0.00% <ø> (ø)
src/buffer.jl	30.40% <0.00%> (ø)
src/framebuffer.jl	0.00% <0.00%> (ø)
src/vertexarray.jl	50.79% <0.00%> (-0.80%)	⬇️
src/shader/shader.jl	31.57% <25.00%> (ø)
src/texture.jl	46.34% <43.43%> (-2.38%)	⬇️
src/for_moderngl.jl	50.00% <68.00%> (+2.22%)	⬆️
src/shader/program.jl	38.40% <100.00%> (ø)
src/context.jl	56.00% <0.00%> (-7.64%)	⬇️

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